Duff's early career started by making guest appearances on made-for-television films such as True Women and on TV series such as The Amanda Show. In addition to guest-starring roles on Chicago Hope, Boston Public, and Third Watch, Duff became a familiar face starting in late 2002 as Amy Sanders on Lizzie McGuire. In 2004, Duff made a guest appearance on That's So Raven as Katina Jones. After making guest appearances on television, Duff received her first role in a feature film when she was cast as Summer Wheatley in Napoleon Dynamite. The film earned her first Teen Choice Award win. She continued making guest appearances, which include Joan of Arcadia and American Dreams. She also lent her voice talent to the Christmas animation film In Search of Santa which again, featured sister Hilary. In 2005, Duff joined the cast of the television series 7th Heaven, playing Sandy Jameson, best friend to Simon's girlfriend Rose.