Mariclare Costello, a lifetime member of The Actors Studio who recurred as the schoolteacher Rosemary Hunter on The Waltons and played a hippie vampire in the cult horror film Let’s Scare Jessica to Death , died April 17 in Brooklyn, her family announced . She was 90.

A native of Illinois, Costello was an original member of the Lincoln Center Repertory Company, and she appeared four times on Broadway , including in a 1970 revival of Harvey that starred Jimmy Stewart and Helen Hayes.

In 1974, she portrayed the wife of Martin Sheen’s title character in the Emmy-winning ABC telefilm The Execution of Private Slovik .

She was married to actor Allan Arbus , who played the psychiatrist Maj. Sidney Freedman on CBS’ M*A*S*H , from 1977 until his death in 2013 at age 95. (His first wife was the photographer Diane Arbus.)

Costello stood out as Rosemary on 15 episodes of CBS’ The Waltons during its first five seasons (1972-77).…