Monster (2003)

Shortly after moving to Florida, longtime prostitute Aileen Wuornos (Charlize Theron) meets young and reserved Selby Wall (Christina Ricci) and a romance blossoms. When a john (Lee Tergesen) attempts to brutalize Aileen, she kills him and resolves to give up prostitution. But supporting herself and her new girlfriend through legitimate means proves extremely difficult, and she soon falls back on old ways. More johns die, and Selby can't help but think her new friend is responsible.