Leifer was born in East Williston, New York, to an Ashkenazi Jewish family, the daughter of Anna Leifer, a psychologist, and Seymour Leifer, an optometrist. As a child, Leifer would frequently put on performances for her family and friends in her family's basement. Leifer recalls her family being a significant part of her fondest memories, including her father's well-known jokes amongst family and friends, as well as her brother taking her to see The Beatles in concert at Shea Stadium