At 2008 Nike Outdoor Nationals as a junior at Lake Park High School, placed 10th in 2 miles in 10:36.73.

[2][3] Flanagan placed 4th in 2 mile at 2009 Nike Indoor Nationals in Reggie Lewis Track and Athletic Center in 10:27.79.

Flanagan finished 4th behind Mamitu Daska Molisa of Ethiopia, Fate Tola of Germany, and Sarah Jebet of Kenya at 2016 Frankfurt Marathon in a new personal best time 2:29:28.

[8] In Fall 2017, Flanagan left Washington, D.C., Mizuno and Riadha Elite Development Program to join Boulder Track Club and Nike.

Flanagan placed 13th in 56:30 in 2018 Cherry blossom 10 mile, 2nd at 2018 Bay to Breakers 12 km in 40:44, and 9th at 2018 USA Half Marathon Championships in 1:14:15.