Greer made her film debut in the horror film "Stricken" (1998), in which she played a college student involved in a fatal prank. This was followed by a small role in the Chicago-filmed drama "Kissing a Fool" (1998). She was cast in her first major role as Fern Mayo, a nerdy teenager who uncovers her classmates' murder of their friend, in Darren Stein's black comedy "Jawbreaker" (1999). The film went on to earn a cult following. Greer followed this with small parts in the romantic comedy films "What Women Want" (2000) and "The Wedding Planner" (2001), opposite Jennifer Lopez. She was cast in a 2002 pilot for NBC alongside Stephen Colbert, "Untitled Ken Finkleman Project" (Imagine Entertainment), based on the Canadian show "The Newsroom" from Ken Finkleman. Colbert portrayed Finkleman and Greer played his sister.