While at Providence College, she became a two-time NCAA Champion in the 5000m and set the collegiate indoor record for women in the same event.

Sisson started running in the seventh grade, and while still in middle school, she won a silver medal in the 3000 metres at the USATF National Junior Olympic Championships in 2005.

[6] After transitioning to high school, Sisson won multiple state championships in track and cross country in Nebraska.

[7] As a freshman in 2006 at Marian High School, she won the state cross country championship in the fall and the 3200m in the spring.

However, Sisson did not participate in her final high school track season, choosing instead to prepare for the 2010 IAAF World Cross Country Championships in Bydgoszcz, Poland.

She decided to transfer to Providence College in Rhode Island after her freshman year, explaining that her experience at Wisconsin was "not a good fit" and citing the opportunity to train under coach Ray Treacy.

[13] As a professional athlete, Sisson continued to train under her collegiate coach, Ray Treacy, while pursuing an MBA at Providence College.

[14] 2015 - 2016 Sisson made her professional racing debut with New Balance at the 2015 USA Outdoor Track and Field Championships, where she participated in the 10000m and finished fifth.

[15] On 20 September 2015, she took part in the 5 km Road Running Championships in Providence, Rhode Island, finishing third.

[17][18] At the US 10 km Championships on 10 October 2016, Sisson captured her first national title, winning by 44 seconds in front of Sarah Pagano.

Her debut performance ranked among the top five fastest times ever recorded by an American woman in the half marathon.

Prior to this, only two American athletes, Molly Huddle and Shalane Flanagan, had recorded faster times.

She finished fifth in the Valencia Half Marathon, clocking 1:07:26 and missing the American record in the event by one second.

She won the race, setting a meet record and qualifying for the 2020 Summer Games in Tokyo.

[41] This performance broke Deena Kastor's 16-year-old record by 43 seconds, and it marked the first time an American woman finished under 2:19 in the marathon.

On 15 January, Sisson ran 1:06:52 in the Houston Half Marathon, bettering her own American record in the event by 19 seconds.

[47] She finished as runner up to Fiona O'Keeffe and ahead of Dakotah Lindwurm, both of whom also made the Olympic team.

[48] Her father, Mark Sisson, was a runner for the University of Wisconsin–Madison from 1979 to 1983 and a 4:02 miler;[6] her mother was a competitive gymnast.