After working on her thesis at Princeton, Halldorson coached girls' volleyball, basketball and softball through the Wayzata School District in Wayzata, Minnesota. In 1987, Princeton head coach Bob Ewell contacted Halldorson and asked her to become an assistant coach with the Tigers' program.[3]
Halldorson later became a head coach at Colby College. As head coach of the White Mules, the team was one of only two non-Division I schools in the 12-team Eastern Collegiate Athletic Conference. In 1995–96, Halldorson led the White Mules to a 12-9-1 overall record.
On November 2, 1997, Halldorson coached her first game with the Minnesota Golden Gophers. The team played in front of a women’s intercollegiate hockey record crowd of 6,854. Halldorson was successful in leading the Gophers to winning its inaugural game. The result was an 8-0 triumph over Augsburg College. In the postseason, the Gophers finished fourth in the first-ever women’s ice hockey national championship. Halldorson was named the inaugural AHCA Coach of the Year in 1998.[4]
On November 2, 2002, Halldorson won her 200th career game. Her last season with the Minnesota Golden Gophers was in 2006–07. Halldorson led the Golden Gophers to a third-place finish in the Western Collegiate Hockey Association regular season. In the postseason, her team defeated Bemidji State in the first round. In the semi-finals, the Gophers defeated Minnesota Duluth, 3-2 in overtime to advance to their fifth-straight WCHA Championship game. The WCHA championship would be Halldorson’s last game as Gophers coach. It was a 3-1 loss to Wisconsin in the title game. Halldorson’s record was 23-12-1 overall and 17-10-1 in conference office. Despite losing the WCHA championship, the Gophers were ranked ninth overall nationally.
