Ms. Ellstein's bigger success on Broadway was the 1953 play, The Fifth Season, a comedy about the dress business, which ran 654 performances. She was co-librettist of a 1950 musical called Great To Be Alive!, and penned the libretto for the 1962 opera, The Golem, by her husband-composer Abraham Ellstein, who died in 1963.
Ms. Ellstein — whose plays were under the name Sylvia Regan — had been a childhood friend of Group Theatre's Clifford Odets and wrote numerous plays including Every Day But Friday, A Hundred Million Nickels, Safe Harbor, 44 West, The Twelfth Hour and Zelda.
As an actress, Ms. Ellstein made her debut under the name Sylvia Hoffman (he birth name was Sylvia Hoffenberg) in a 1926 and later appeared in The Waltz of the Dogs and Poppa. She was promotions and public relations manager for the Theatre Union at the Civic Repertory Theatre (1932-26) and the Mercury Theatre Company (1936-38).
Before marrying Ellstein, her first marriage to James J. Regan ended in divorce.