In September 2017, Pettyjohn was cast as Laura Dern's daughter in the movie Trial by Fire. Additionally, she was added to the cast of the crime thriller film Destroyer, and appeared in the film Against All Enemies. In late 2018, Pettyjohn was cast in Deadwood: The Movie, playing the role of Caroline, a newcomer to the town of Deadwood. In 2019 she was cast in the Hulu television series Little Fires Everywhere playing Lexie Richardson, the daughter of Reese Witherspoon's character. In June 2020, it was announced that Pettyjohn had been cast in the ABC television drama series Big Sky, playing Grace Sullivan who is kidnapped along with her older sister Danielle (Natalie Alyn Lind).
