McMahon was drafted by Fremantle with their third selection, and 35th overall in the 2019 AFL Women's draft.
On Christmas Eve in 2019, McMahon was working as a police officer and was hit by a stolen car whilst attempting to stop the car using spike strips.[1] She suffered a broken left fibula and a torn anterior cruciate ligament on her right leg and was unable to play for the 2020 and 2021 seasons.[2] She made her AFLW debut in the opening round of 2022 AFL Women's season 6.[3]
McMahon was delisted by Fremantle in April 2022.[4]