Posey is the cousin of actor-musician Tyler Posey and niece of actor John Posey. She appeared as Becky in HBO teenage drama series Euphoria. She appeared in the feature films Gully (2019), and Dreamcatcher (2021).

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On television, she appeared in comedy series It’s Always Sunny in Philadelphia, and had a recurring role on Starz series Heels. In March 2025, she joined the cast of Vought Rising, a spin-off prequel series from superhero television comedy series The Boys, portraying Private Angel.