In 2003, Krieger started in all 25 matches for Penn State, ten of those appearances being in conference matches. She ranked fifth in number of shots in the season at Penn State with 24 and third in assists with nine. Penn State was the 2003 Big Ten Conference regular season champion and was No.1 seed in the Big Ten Women’s Soccer Tournament. Krieger started in the quarterfinals of the tournament, where they faced Wisconsin on November 6. Wisconsin advanced in the tournament on penalty kicks after the scored was tied 0–0. Penn State earned the No. 5 seed in the NCAA Tournament, its highest seed up to that point. They made it to the quarterfinal round, when they were defeated by UCLA on November 28, 2003. At the end of the 2003 season, Krieger was named Big Ten Freshman of the Year. Krieger broke the big ten record for numbers assist in one game with four against Bucknell on September 17, 2003.

In 2004, Krieger started in all 23 matches for Penn State, ten of those appearances being in conference matches. She ranked fourth in points for the season with nine, fifth in goals with three, sixth in assists with three, fourth in shots with 35, and third in shots on goal with 16. Penn State was the 2004 Big Ten Conference regular season champion and was No.1 seed in the Big Ten Women’s Soccer Tournament. Krieger started in all three matches of the tournament for Penn State. Penn State faced Ohio State on November 7 in the final of the tournament, which ended in a 0–2 defeat for Penn State. Penn State earned the No. 2 seed in the NCAA Tournament, its highest up to that point. They made it to the second round, where they were defeated by Maryland on November 14. At the end of the 2004 season, Krieger was given NSCAA All-Mid-Atlantic Region First Team honors, All-Big Ten First Team honors, and Academic All-Big Ten honors.

During her senior season, Krieger was named captain of the team and switched from the midfield position to defense. She played in all 19 games for Penn State, eight of those being in conference matches. She made one goal and two assists during the season. Penn State was the 2006 Big Ten Conference regular season champion and the No. 1 seed in the Big Ten Women’s Soccer Tournament. Krieger appeared in all of the team’s matches in the tournament, including the final against Illinois on November 5, helping Penn State win the tournament. Penn State earned a No.2 seed at the NCAA Tournament and made it to the quarterfinals, when they were defeated by Notre Dame on November 24. At the end of the 2006 season, Krieger was named Big Ten Defensive Player of the Year and Penn State’s Most Valuable Player. She also received NSCAA All-Mid-Atlantic Region First Team honors, NSCAA All-America First Team honors, All-Big Ten First Team honors, Big Ten All-Tournament Team honors, and Academic All-Big Ten honors. After being named to the NSCAA All-America First Team in both 2005 and 2006, Krieger became the only Nittany Lion to be given All-American honors at two different positions.

Following her short time with the Northern Virginia Majestics in the summer of 2005, Krieger returned to the Washington Freedom in July 2005 for more exhibition matches with the team. In November 2005, Krieger sustained a broken leg while with her collegiate team and eventually developed a pulmonary embolism, which kept her off the pitch that summer. In order to recover and refrain from further traveling, Krieger remained at Penn State and did not join the Washington Freedom for their 2006 season. Krieger joined the Freedom during the summer of 2007 for their first season as a full W-League team.

Krieger is very close with her brother, Kyle. He is a YouTube and Instagram personality who has talked openly about his previous drug and alcohol problems. Although he was at an all-time low during Krieger’s life-threatening pulmonary embolism in 2005, Kyle has been sober for twelve years and has been a support system for Krieger through her recent injuries. Regarding her relationship with her brother, she has stated: “I have fallen a few times and each time I have gotten up and grown as a person and looked at things a little differently. That is where I have learned so much from Kyle. (Seeing him) struggling through addiction and alcoholism and overcoming that and overcoming adversity, for me that’s just an unreal role model in my life. It is like night and day. For two years of my life he was absent, in and out of my life. To look at how far he has come it is just so rewarding to see.”

In August 2007, immediately following the W-League season, Krieger signed a two-year contract with 1. FFC Frankfurt in the Frauen-Bundesliga, the highest division of women’s soccer in Germany. Her first season with the team was the 2007–08 season, which ran from August 19, 2007 to June 15, 2008. During the season, Krieger helped FFC Frankfurt become Bundesliga Champions, Frauen DFB–Pokal Champions, and UEFA Cup Champions. Krieger became the first American to win the UEFA women’s cup.

Krieger became a professional athlete with Nike in 2007 and exclusively wears Nike cleats and training gear. Krieger and teammate Sydney Leroux introduced Sydney + Ali’s Dynamic Duo Workout on the Nike+ Training Club app in 2014. In 2015, Krieger appeared in the Nike+ Training Club 90-Day Better For It Challenge alongside teammates Carli Lloyd and Christen Press. The campaign combined various Nike+ workouts into a fitness program.

In September 2008, Krieger was one of the 21 United States national team players who was allocated to a team in the newly formed Women’s Professional Soccer (WPS) league. However, due to her commitments with FFC Frankfurt, Krieger was unable to join the team at the time. Instead, she stayed in Germany for the 2008–09 Bundesliga season, which ran from August to June. Early on in the season, Krieger sustained an injury to her foot that limited her movement. At the end of the Bundesliga season in June 2009, Frankfurt allowed Krieger to joined the Washington Freedom on loan for the 2009 season, where she could adequately recover and regain fitness for the following Bundesliga season.

Krieger was first called up to the United States women’s national team in January 2008 for a six-day training camp at The Home Depot Center in Carson, California from January 3 to 8. Immediately following the training camp, Krieger was named to the roster for the 2008 Four Nations Tournament held from January 16 to 20. Regarding her first roster appearance for the national team, Krieger stated that she felt “honored to be a part of the first roster of 2008, to be a part of this team and represent not only myself but my country.” Krieger made her first appearance for the national team on January 16, 2008 in the team’s first match of the Four Nations Tournament against Canada. Krieger started the match and played all 90 minutes, helping the United States defeat Canada 4–0. She made one other appearance during the tournament on January 18 in the match against Finland, a 4–1 in for the United States. The United States went on to win the tournament after a 1–0 victory over China. Krieger then went back to her club team, FFC Frankfurt, and did not join the national team again until late May for a training camp.

On June 23, 2008, Krieger was named an alternate for the 2008 Summer Olympics.

Krieger made her first appearance for the Washington Freedom in the 2009 WPS season on June 13 in a match against the Chicago Red Stars. She started the match and was replaced in the 72nd minute by Jill Gilbeau. Krieger made a total of 10 appearances in the regular season, starting nine. She recorded one assist. The Washington Freedom went on to place third in the WPS and advanced to the playoffs. In the first round of the playoffs on August 15, the Freedom faced Sky Blue FC. She started the match and played all 90 minutes. The Freedom were defeated 1–2 and were eliminated from the playoffs.

Following the WPS season, Krieger returned to Germany to play with FFC Frankfurt for the 2009–10 season, starting with a match on September 20, 2009 against VfL Wolfsburg. She made 15 appearances in the regular season to help FFC Frankfurt finish third in the Bundesliga. Due to their third-place finish, Frankfurt did not qualify for UEFA Champions League. Krieger also appeared during two matches of the Frauen DFB–Pokal on November 14 and December 19. In February 2010, Krieger’s contract with Frankfurt was extended for an additional year until June 2011.

In May 2010, Krieger was named to a 22-player roster for a match against Germany on May 22. She made her first appearance with the national team since January 2008 during the match against Germany. Krieger came in for Heather Mitts in the second half to help the United States win the match. Krieger was then named to a 24-player roster for a pair of matches against Sweden in July. Krieger came in during the 77th minute of the first match on July 13 for an injured Amy LePeilbet. She made the start in the second match on July 17.

Krieger played with Frankfurt for the 2010–11 season, appearing in 14 matches in the regular season to help Frankfurt finish second in the Bundesliga. She also appeared in four of Frankfurt’s matches in the Frauen DFB–Pokal, including the final against Turbine Potsdam on March 26, 2011. Frankfurt won the final 2–1 to take the title. In March 2011, Krieger decided to return to the United States in order to focus on training with the United States women’s national team.

Following the 2011 FIFA Women’s World Cup, Krieger returned to Germany for the 2011–12 Bundesliga season. Her first appearance for the team since the previous March was on August 21, 2011 against SGS Essen. She subsequently made 18 appearances for the team between August and December, three of those appearances being a part of the Frauen DFB–Pokal. In January 2012, Krieger sustained a serious knee injury while with the United States national team that kept her off the pitch for the rest of the season.

On October 13, Krieger was named to the roster for the 2010 CONCACAF Women’s World Cup Qualifying tournament held from October 28 to November 8. With six caps for the national team, she was one of the least experienced players on the roster. Both of her appearances during the tournament were in matches against Costa Rica. The United States placed third place in the tournament and earned a berth in a two-game series against Italy to qualify for the last spot in the 2011 FIFA Women’s World Cup. Krieger was named to the roster for those two matches on November 20 and 27. She came in for Heather Mitts during the 75th minute in the first match and the 76th minutes in the second match to help the United States qualify for the 2011 FIFA Women’s World Cup.

Following a six-month recovery, Krieger made her first appearance back with FFC Frankfurt on September 23, 2012 in a match against Bayer Leverkusen, a 4–2 win for Frankfurt. She appeared in seven matches for Frankfurt, one of those being in the Frauen DFB-Pokal. In December 2012, Krieger requested and was granted release from her contract in order to play in the newly formed National Women’s Soccer League.

On January 11, 2013, Krieger was allocated to the Washington Spirit during the 2013 NWSL Player Allocation for the inaugural season of the National Women’s Soccer League along with goalkeeper Ashlyn Harris and midfielder Lori Lindsey. Krieger made her first appearance for the Spirit on April 14, 2013 in a match against the Boston Breakers that ended in a 1–1 draw. She made 18 appearances in the regular season, starting 16. In her 1,412 minutes with the Spirit, she scored one goal. The Washington Spirit finished the season in last place in the NWSL.

In August 2013, it was announced that immediately following the NWSL regular season, Krieger would be joining Tyresö FF in the Damallsvenskan, the highest division of women’s soccer in Sweden. Krieger, Spirit teammate Ashlyn Harris, and United States women’s national soccer team teammate Whitney Engen all signed short-term contracts with the team. They joined other United States national team members Christen Press and Meghan Klingenberg, who were already with the club on long-term contracts. Four days after the end of the NWSL season, Krieger played her first game for Tyresö on August 21, 2013. She made seven appearances with the team in the Damallsvenskan regular season and four appearances in the UEFA Women’s Champions League.

Krieger made her return to the national team in January 2013, when she was called up to a 29-player training camp leading up to two matches against Scotland in early February. On February 21, Krieger was named to the 23-player roster for the 2013 Algarve Cup in Portugal that took place from March 6 to 13. On March 8, Krieger made her first international goal in the match against China. She was subsequently named Budweiser Woman of the Match. She also started in the match against Sweden on March 11 and the final match on March 13 to help the United States win the Algarve Cup title.

Following the 2013 Algarve Cup, Krieger traveled to Europe with the national team for matches against Germany and the Netherlands in early April. She appeared during the match against the Netherlands on April 9, a 3–1 win for the United States. In late May, Krieger was named to the 21-player roster that traveled to Canada to train in preparation for a match against Canada on June 2. She played all 90 minutes of the match to help the United States defeat Canada 3–0.

On January 3, 2014, Krieger was once again allocated to the Washington Spirit for the 2014 season. She made 22 appearances in the regular season, starting all 22. In the 1935 minutes she played for the Spirit, she made one goal and one assist, helping the Spirit finish fourth and advance to the playoffs. The Spirit faced Seattle Reign on August 24 in the semifinal. Krieger played all 90 minutes of the game, which ended in a 2–1 defeat for the Spirit.

Krieger teamed up with the charity MiracleFeet in 2014. MiracleFeet is an organization that works to treat children with clubfoot in developing countries. Regarding her involvement with MiracleFeet, Krieger stated that it “means the world to [her] to be able to have this opportunity to help transform a kid’s life.”

Krieger was once again with the Washington Spirit for the 2015 season. During the team’s league opener on April 10, 2015, Krieger suffered a concussion in the 17th minute after making contact with the head of Jessica McDonald as they both jumped for a header. Krieger missed two matches with the Washington Spirit before she returned to training. However, she did not appear in another match for the Spirit until after the 2015 FIFA Women’s World Cup, as she left to train with the United States women’s national team soon after her recovery. She returned to the Spirit in late-July, appearing in a match against the Chicago Red Stars on July 25, which ended in a 1–1 draw. Krieger made eight appearances for the Spirit in the regular season, playing a total of 655 minutes. The Spirit ended the season in fourth place, clinching a spot in the playoffs. They faced Seattle Reign in the semifinals on September 13. Krieger was attending her father’s wedding in Virginia the week of the playoffs and missed the match against Seattle Reign. The Spirit were defeated 3–0, eliminating them from the playoffs.

Krieger started off the year at a 21-day training camp in 2015 from January 5 to 25 at the U.S. Soccer National Training Center in Carson, California. Following the training camp, Krieger was named to the 24-player team that would travel on a 13-day trip to Europe for matches against France and England in mid-February. Krieger came in during the 55th minute of the match against France on February 8. She also played all 90 minutes in the match against England on February 13, which was a shutout victory for the United States.

On April 14, 2015, Krieger was named to the 23-player roster that would represent the United States at the 2015 FIFA Women’s World Cup. She started all seven games of the tournament for the United States and played all but 10 minutes. She was a part of the defense that allowed three goals in all seven games and recorded five consecutive shut outs. Krieger became a World Cup Champion on July 5, when she helped the United States defeat Japan 5–2 in the Women’s World Cup final. Krieger joined the national team on a Victory Tour following their World Cup win that started in Pittsburgh, Pennsylvania on August 16 and ended in New Orleans, Louisiana on December 16.

In June 2015, Krieger became an ambassador for the non-profit organization Athlete Ally, which works to end homophobia and transphobia in sports. Krieger believes creating an accepting environment on and off the field, as Athlete Ally strives to do, is important for athletes and is the reason she joined the organization.

Following the concussion she sustained while with the Washington Spirit in April 2015, Krieger teamed up with Unequal, which makes protective sports gear. When she returned to play following the concussion, she wore a protective headband provided by Unequal.

Krieger returned for her fourth season with the Spirit in 2016, playing 15 games, 14 starts, during the regular season and all 120 minutes of both postseason matches. She scored two goals, including the first goal in the semifinal which gave the Spirit the early lead in what would end up being the first semifinal win in the club’s history. Krieger recorded an assist on one of Crystal Dunn’s goals in the NWSL Championship. She was voted Spirit Fan Favorite and Spirit Defender of the Year and named to NWSL Second Best XI.

On November 2, 2016, it was announced that Krieger had been traded to the Orlando Pride in exchange for the Pride’s spot in the Allocation Ranking Order, which determines how elite players are allocated throughout the NWSL. She joined national team players Alex Morgan and Ashlyn Harris, who had also previously played with the Spirit until the 2015 expansion draft. Krieger stated the following day that she was surprised by the trade, but was ready to embrace new opportunities in Orlando.

On July 12, 2016, Krieger was named to the 18-player team that would represent the United States at the 2016 Olympic Games in Rio de Janeiro. She made her Olympic debut on August 6 in the team’s second group match against France. She replaced Crystal Dunn in the 70th minute to help the United States secure their first-place finish in the group with a 1–0 victory over France. On August 9, Krieger played all 90 minutes of the team’s final group match against Colombia.

In 2017 Krieger started every game for the Pride, helping Orlando finish 3rd in the standings and qualify for the playoffs for the first time. Krieger was named to the 2017 NWSL Best XI.

In 2017 Krieger received limited call-ups and only appeared in two games. She was on the roster for the 2017 Tournament of Nations but did not appear in any games.

Following the 2018 NWSL season, Krieger was one of 21 NWSL players who participated in a series of coaching licensure courses co-sponsored by U.S. Soccer, the NWSL, and Utah Royals FC. Krieger, who earned who U.S. Soccer “C” license following the course, has expressed interest in coaching at the professional or national team level.

In May 2019, despite earning only one cap in the previous 25 months, Krieger was named to the final 23-player squad for the 2019 FIFA Women’s World Cup, marking her third World Cup appearance. She earned her 100th cap for the national team on May 16, 2019, coming on as a second-half substitute in the team’s warm-up friendly against New Zealand. Krieger made three appearances during the tournament including as a halftime substitute during the final against the Netherlands as the USWNT won 2–0 to successfully defend its World Cup title.

On March 13, 2019, Krieger announced her engagement to long time girlfriend Ashlyn Harris. Harris is also a soccer player who plays with Krieger on the Orlando Pride and the national team. The two got married on December 28, 2019 in Miami.

she was also named for the roster to She believes Cup tournament that held in early 2020.