Sullivan played college soccer for the Stanford Cardinal, where she won an NCAA championship and the Hermann Trophy in 2017.

Raised in Lorton, Virginia, Sullivan is the youngest of four siblings and attended South County High School.

As a senior, Sullivan tallied three goals and six assists and led Stanford to their second national championship, scoring in the College Cup final.

Sullivan was named a finalist for NWSL Rookie of the Year, finishing second in voting behind winner Imani Dorsey.

[12] She went on to captain the Spirit to the club's first-ever NWSL Championship title in a 2–1 comeback victory over the Chicago Red Stars.

Sullivan converted the match's equalizer in the 67th minute, firing a penalty kick past opposing goalkeeper Cassie Miller to draw the two teams level.

The Washington Spirit later announced that Sullivan had torn her ACL and would be placed on the season-ending injury list, missing the rest of the regular season and playoffs.

[3] Sullivan competed for the United States at the 2012 CONCACAF Women's U-17 Championship in Guatemala where she helped the under-17 national team win gold.

[21] She missed a large part of the year due to the injury but made her return to the national team on October 19, 2017.

[31] After not being in the squad for the 2019 FIFA Women's World Cup or 2020 Summer Olympics, Sullivan was called back in to the national team by head coach Vlatko Andonovski.

Alongside fellow non-olympians Mallory Pugh and Sophia Smith, Sullivan was added to an absence-heavy squad[32] for two September 2021 friendlies against Paraguay.