While studying at Christian Brothers University, Gregg played for the school's soccer team.[5] During her tenure, the team earned a Division II National Championship title.[6] Although she only played in 47 games, she holds, as of 2022, she holds seven National Collegiate Athletic Association (NCAA) records, including total number of goals scored in a single season (73), points in a single season (156), career points (287), and career goals (180), as well as average points per game (7.09) and goals per game in a season (3.32), and goals per game for career (2.81).[2] She was also named the NSCAA/Adidas national Player of the Year in 2001 and 2002,[4] becoming the first player, regardless of gender, two receive the award more than once,[6] and was named the Gulf South Conference Player of the Year in 2001 and 2002.[2][4] For the 2002–2003 school year, she won the Honda Sports Award.[4]
In 2003, Gregg stated she intended to remove herself from the WUSA draft to focus on healing a torn knee ligament.[5] However, she was selected in the third round to play for the Washington Freedom, where she would be on loan for a minor league team or remained unsigned for the following season.[5] WUSA folded at the end of the season.