Born in Manhattan, Michaelsen followed her parents into show Business. Her father, Arne Markussen, is a singer. Her mother, Roberta Stevenson, was a Dancer. She sang on the Soundtrack for Sesame Street and was performing in Off-Broadway plays by age 11. In 1975 her family moved to Beverly Hills and Michaelsen (who changed her name from Markussen) soon won guest spots on such shows as Diff'rent Strokes and Eight Is Enough. Her father is of Norwegian heritage.