Seidel was invited to the Bupa Great Edinburgh International Challenge in Scotland where she placed third (15:16) in the 4K and was the first USA high school finisher.

Seidel was invited to the 2012 Bupa Great Edinburgh International Cross Country in Scotland where she placed third (15:16) in the 4 km and was the first USA high school finisher.

[11][12] Seidel qualified to represent Team USA at the 2018 Great Edinburgh International Cross Country in Scotland.

She qualified for Team USA at 2018 NACAC Cross Country Championships in La Libertad, El Salvador on February 17, 2018.

[13] In Atlanta, Georgia, at the U.S. Woman's Olympic Trials Marathon on February 29, 2020, Seidel broke from the pack along with Aliphine Tuliamuk.

[16] Seidel finished fourth at the 2021 New York City Marathon with a time of 2:24:42, which was the fastest ever by an American woman.

[17] In 2021, Molly Seidel participated in the Berbee Derby held in Fitchburg, Wisconsin and set the record for the fastest run for an individual dressed as a turkey.

In her first marathon start in eighteen months, Seidel finished in eighth place, the second American, in a personal best time of 2:23:07.