O'Sullivan made her debut in the State Basketball League (SBL) in 2011 for the Perth Redbacks.

[5] Upon returning to Australia after graduating from CCGA, O'Sullivan was intrigued by the hype surrounding women's football and was convinced by her father John to play for East Fremantle – the club he represented in league football on 133 occasions.

[6] She impressed for the Sharks, and as a result, her name made its way to Fremantle women's head coach Michelle Cowan.

O'Sullivan was recruited by Fremantle as a pre-draft rookie selection,[6] and made her debut in a thirty-two point loss to the Western Bulldogs at VU Whitten Oval in the opening round of the 2017 season.

[8] In August 2022, to open the AFL Women's season seven, O'Sullivan played her 50th game for Fremantle.