At age fifteen, Schroeder became the youngest founding member of the All-American Girls Professional Baseball League, thus having the distinction of being the only girl to play in the league for its twelve full seasons. A three-time All-Star and ranked in the Top-10 in several offensive categories, she was arguably the top shortstop in league history. After the league folded in 1954, she played four more years on a touring team of 11 All-Americans piloted by Bill Allington across Canada and United States. When the lack of finances caused the tour to end after four summers, Schroeder had played a record 15 seasons of professional baseball.
Schroeder enjoyed her most productive season in 1954, when she posted career-highs with .304, 17 homers and 65 runs batted in. In that season, she was part of a Lassies All-Star slick infield that included June Peppas at first base, Nancy Mudge at second, and Fern Shollenberger at third. Meanwhile, the called Home Run Twins, Chris Ballingall (17) and Carol Habben (15), powered the offense with 32 home runs; Peppas enjoyed a year career, and Kalamazoo advanced to the Championship Series. As a result, the Lassies defeated the Daisies in a best-of-five games series, with a decisive eight-inning RBI double by Schroeder in Game 5, during what turned out to be the AAGPBL final season.