Gilbert was born Sara Rebecca Abeles in Santa Monica, California, the daughter of Barbara Cowan (née Crane) and Harold Abeles. Both her parents are Jewish. Her maternal grandfather is The Honeymooners creator Harry Crane. Gilbert has four older half-siblings. Her two siblings on her mother's side, Melissa Gilbert and Jonathan Gilbert, were stars of Little House on the Prairie. In 1984, Sara took the last name Gilbert for Paul Gilbert, her mother's first husband. Gilbert also has two siblings on her father's side, sister Patrice and brother Joseph.