The Diary of a Teenage Girl is Heller's debut film, that she both wrote and directed, which premiered at the Sundance Film Festival on January 24, 2015. The film later received a limited release in August 2015. It is based on the 2002 graphic novel titled The Diary of a Teenage Girl: An Account in Words and Pictures by Phoebe Gloeckner. The film stars Bel Powley as Minnie, a 15-year-old girl living in the San Francisco Bay Area in 1976 who begins an affair with her mother's 35 year-old boyfriend Monroe.