After moving to Los Angeles, Kidder was cast opposite Gene Wilder in Quackser Fortune Has a Cousin in the Bronx (1970) as an exchange student in Ireland who becomes the love interest of a poor horse manure collector in Dublin whom she almost runs over with her car. After filming in Ireland, Kidder relocated to New York City to further study acting. A year later, she returned to California, and was cast in the Brian De Palma cult classic Sisters (1973), which gained notoriety for both director and Kidder, who as leading lady, portrayed conjoined twins. Kidder had been in a relationship with De Palma at the time, and had been roommates with co-star Jennifer Salt in Los Angeles. She then starred in the slasher film Black Christmas in 1974, for which she won a Canadian Film Award for Best Actress; followed by a role as a prostitute in the Terrence Malick-scripted The Gravy Train (1974). She received another Canadian Film Award for Best Actress for her performance in the war drama A Quiet Day in Belfast (1974).