In 2013, Gareis attended a U15 Girls' U.S. Youth National Team Training Camp. Gareis was a member of Illinois' Olympic Development Program (ODP) in 2010 and 2014. Gareis played for the Illinois ODP team when they played in the National Championships in 2014.
In December 2021, Gareis was selected by the Houston Dash in the fourth round of the 2022 NWSL Draft.[3] On February 18, 2022, Gareis signed a two-year contract with Houston.[4] She made 20 appearances for the Dash in the 2022 season, and was named the club's Young Player of the Year.[5] In January 2023, she signed a contract extension with Houston.[6]
She and Pat Connaughton announced their relationship in June 2023.[8] In January 2024, they announced Gareis was pregnant.[9] They got engaged in February 2024.[10]