At the 2024 Paris Olympics, Gemmell, along with Claire Weinstein, Katie Ledecky, and Paige Madden, won the silver medal in the 4x200m freestyle relay.

[12] In April, at the 2022 USA Swimming International Team Trials in Greensboro, Gemmell swam 2022 Junior Pan Pacific Swimming Championships qualifying times in the 200 meter freestyle, a 1:58.12, and the 400 meter freestyle, a 4:13.63, and was named to the United States roster in both events.

[13][14] Three months later, in July at the 2022 US National Swimming Championships in Irvine, she won the silver medal in the 200 meter freestyle with a personal best time of 1:56.14, finishing 1.64 seconds behind gold medalist Katie Ledecky.

[15][16][17][18] Two days later at the Championships, she won the national title and gold medal in the 400 meter freestyle with a personal best time of 4:06.17.

[25][26] She lowered her Championships record and personal best time to 54.13 seconds in the final, winning the gold medal.

[38] For her second FINA Swimming World Cup, Gemmell started off with a personal best time of 4:01.35 in the preliminary heats of the 400 meter freestyle at the 2022 FINA Swimming World Cup in Indianapolis, dropping 1.93 seconds from her former previous best time and qualifying for the final ranking third.

[41] The next morning, she ranked fifth in the preliminary heats of the 200 meter freestyle, qualifying for the final with a personal best time of 1:54.31.

[8][52][53] For the third morning preliminaries, Gemmell contributed a 24.34 for the second leg of the 4×50 meter freestyle relay to help qualify for the final ranking third.

[8][57][58] At the 2023 Metro Championships in February in Boyds, Maryland, Gemmell contributed to an overall win for her school's team, Stone Ridge, with a new competition record and personal best time of 1:43.45 in the 200 yard freestyle that won the event, and a personal best time of 48.19 seconds in the 100 yard freestyle that won her the title in that event as well.

[59][60] At the 2024 Paris Olympics, Gemmell competed along with Claire Weinstein, Katie Ledecky, and Paige Madden in the 4x200m freestyle relay.