lavin was born in portland, maine, the daughter of david joseph lavin, a businessman, and lucille ("née" potter), an opera singer. the lavin family were active members of the local area jewish community. both sets of grandparents, simon and jessie lavin and harry and esther potter, emigrated from russia. her family was musically talented, and lavin has been onstage since the age of five. she studied acting at hb studio in new york city. she attended waynflete school before enrolling in the college of william & mary. while at william and mary, she performed with the william and mary theater in many productions directed by long-time professor howard scammon. in the summer of 1958, she played one of the leads in "the common glory", an outdoor drama written by pulitzer-prize winning playwright paul green and staged at an amphitheater on campus. upon her graduation from william and mary, she had already received her actors' equity association card. she was a member of the compass players in the late 1950s. by the early 1960s, lavin had appeared in several broadway shows and appeared on the 1966 cast recordings of "the mad show" performing stephen sondheim's "the boy from...". from "it's a bird...it's a plane...it's superman", one of her numbers, "you've got possibilities", was the album's best-received song and was called "the one memorable song...flirty, syncopated" by the "dallas observer".