Born in Cooma, New South Wales, Duncan is known to Australian audiences as a character Actress in television, stage an films, as well as having appeared in television commercials. Australian television roles included several episodes of the Australian series Hunter (1967) and she appeared for several months in the evening soap opera Number 96 playing Helen Sheridan in 1973. From there, a role on the soap Certain Women followed. She later had an ongoing role in Skyways, and guest starred in several episodes of A Country Practice as Rowena Elliott, Terence Elliott's wife. Film roles include playing a lascivious, sadistic and murderous lesbian armed with a crossbow in exploitation film Turkey Shoot (1982).