Mariclare Costello, who played the devoted schoolteacher Rosemary Hunter on The Waltons, a free-spirited hippie-turned-vampire in the 1971 cult horror film Let’s Scare Jessica To Death and appeared in nine Broadway productions during the 1960s, died Friday, April 17, in Brooklyn, her family has announced. She was 90.

Married to M*A*S*H actor Allan Arbus until his death in 2013, Costello received her master’s in theater and education from Catholic University, was an original member of Lincoln Center Repertory Company and a lifetime member of The Actors Studio.

Born February 3, 1936, in Peoria, Illinois, Costello moved to New York City after graduate school and landed roles both Off Broadway and on Broadway. Her Broadway debut came in 1964 with a role in Arthur Miller’s After the Fall opposite Jason Robards. Eight Broadway credits would follow, including But For Whom Charlie (1964), The Changeling (1964), Tartuffe (1965), Danton’s Death (1965), The Country Wife (1965), Lovers and Other Strangers (1968), A Patriot for Me (1969) and Harvey, with James Stewart and Helen Hayes (1970).

Costello made her film debut in 1967’s The Tiger Makes Out starring Eli Wallach and Anne Jackson, then appeared on several TV series including the 1969 cop show N.Y.P.D. before being cast two years later in Let’s Scare Jessica To Death, a moody horror film starring Zohra Lampert as Jessica, a woman just released from a mental hospital who thinks she might be relapsing when ghostly things begin to happen. Costello played the pivotal role of a hippie who takes up with Jessica and her husband only to become a vampire. Among the film’s most memorable scenes is the undead Costello emerging slowly from a lake to attack the title character.

Subsequent credits include the acclaimed 1974 TV movie The Execution of Private Slovik in which she played the wife of Martin Sheen’s title character. In 1980 she played the sympathetic sister-in-law of Mary Tyler Moore’s grieving mother in Robert Redford’s Ordinary People.

Her many TV credits included episodic roles throughout the 1970s, ’80s and ’90s in, among others, Ironside, Kojak, Little House on the Prairie, Lou Grant, Murder She Wrote, Santa Barbara, Chicago Hope, Judging Amy and, in the early 2000s, TV movie Shadow of the Blair Witch and series Providence.

Costello was a series regular on the single-season 1977 CBS drama The Fitzpatricks, but she is probably best remembered for her recurring role over five seasons (1972-1977) of CBS’ hit family drama The Waltons. She played Miss Rosemary Hunter, the kindly school teacher who encourages a young John-Boy Walton (Richard Thomas) to become a writer. The character later married the town’s preacher played by a pre-Three’s Company John Ritter.

She is survived by her daughter, the stage director Arin Arbus, and Arin’s partner, the playwright Ethan Lipton; granddaughter Bird; stepdaughters Amy and Doon; six nieces and a nephew.

A funeral service will be held in New York City, with burial and remembrance in Peoria.