Coulter released "Can't Touch It" as the lead single from her second album Brand New Day in August 2007. The song peaked at number two and remained in the top-ten for eight consecutive weeks. It is Coulter's most successful single, and was certified platinum in 2008. At the 2007 Jägermeister AIR Awards, "Can't Touch It" was nominated for 'Best Performing Independent Single/EP'. Brand New Day was released on 11 August 2007, which peaked at number 37. Coulter worked with several producers and songwriters on the album, including KNS, David Gamson, Marc Nelkin, Vince Pizzinga, Andrew De Sylva, Mtawarira and Glenn Cunningham, among others.
At the 2007 Nickelodeon Australian Kids' Choice Awards, Coulter won the award for 'Fave Female Singer'. Her version of Swedish recording artist Agnes Carlsson's "Love Is All Around" was released as the second single from Brand New Day in November 2007, and peaked at number five. On 18 November 2007, Coulter performed at the first Fluffy Festival in Brisbane alongside acts such as Mr Timothy, Slinkee Minx, Potbelleez, TV Rock, Seany B and Vandalism. A month later, it was announced that Coulter had signed two international record deals, with dance label Ministry of Sound UK and the Japanese independent label Pony Canyon. Brand New Day was released in Japan on 9 January 2008, and peaked at number 242 on the Japanese Albums Chart. That same month, Coulter was a supporting act for Hilary Duff's Australian leg of her Dignity Tour. "Can't Sing a Different Song" was released as the album's third and final single in March 2008, and peaked at number eight. During this time, Coulter embarked on her Brand New Day Tour in Australia, which served as her first solo headlining tour. At the 2008 Nickelodeon Australian Kids' Choice Awards, she received two nominations in the categories of 'Fave Aussie' and 'Fave Singer', and won the latter award. In September 2008, Coulter released "Wiggle It", which peaked at number 11, as the lead single from her first compilation album The Singles. The album was released on 8 November 2008, but failed to impact the charts.
In 2007 and 2008, Coulter was an ambassador for McHappy Day, an annual fundraising event by McDonald's that supports the Ronald McDonald House Charities and provides much needed programs and services to seriously ill children and their families. In 2008, Coulter became the face of Jeans for Genes Day in Australia, a charity fundraising event organised by the Children's Medical Research Institute which sponsors investigation into childhood genetic diseases. Coulter has supported the charity since she was in high school. She raised $100,000 for the campaign, including profits made from her nude photo shoot with Cleo magazine. Alongside recording artist Marcia Hines, Coulter became a spokeswoman for the annual Australian red ribbon appeal in November 2011, raising money in the fight against HIV and AIDS, and helping people with HIV. A month later, on 19 December 2011, she performed at the Pitt Street Mall in Sydney, as part of the Optus Celebrity Carols initiative to raise money for The Smith Family, a charity benefiting disadvantaged children and their families. In 2015, Coulter became an ambassador for McHappy Day again.
At the age of 15, Coulter met Jamie Babbington, a builder from Gold Coast who was aged 23 at the time. They started "dating seriously" after about a year. Coulter and Babbington married at a secret location in Canungra, Queensland on 7 September 2007. Coulter took her husband's last name and became Ricki-Lee Babbington. The couple had their honeymoon in the Maldives for five weeks. The following year, on 18 October 2008, Coulter's publicist issued a statement that they had separated due to "distance and time apart". In an interview with Herald Sun's Jonathan Moran, three years after the marriage ended, Coulter revealed that she had experienced depression during her relationship with Babbington. "I was living my dream but behind closed doors my personal life was a mess. [...] I felt alone, I bottled it all up and it made things worse. I wanted to give up everything. I wouldn't leave the house for days at a time. I'd sit in the house all day and do nothing".