Adler married three times, first to Horace Eliascheff, the father of her only child Ellen, then from 1943 to 1960 to director and critic Harold Clurman, one of the founders of the Group Theatre. She was finally married to physicist and novelist Mitchell A. Wilson, who died in 1973. From 1938 to 1946, she was sister-in-law to actress Sylvia Sidney. Sidney was married to her brother Luther at the time and provided Stella with a nephew. Even after Sidney and Luther divorced, she and Sylvia remained close friends.