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). Her character, the first to read one of John-Boy’s (Richard Thomas) stories at Walton’s Mountain School, winds up marrying the Rev. Matthew Fordwick (John Ritter) on the show’s fourth-season opener in September 1975.

“I had the greatest time with Richard Thomas and John Ritter,” she recalled in a 2011 interview. “We laughed from the beginning of the day until the end of the day. We spent a lot of time together. They were great.”

Costello noted that when she told producers that she was pregnant, they wrote that into the show, and the toddler Arin appears as Rosemary’s daughter, Mary Margaret, in season five.

She left the series to co-star as the matriarch on the 1977-78 CBS drama The Fitzpatricks, a drama about a family with four kids (one of them played by Jimmy McNichol) living in Flint, Michigan. The show, however, lasted just 13 episodes.

In Let’s Scare Jessica to Death (1971), directed by John D. Hancock, Costello was mesmerizing as Emily Bishop, a vampire ghost who terrorizes her mentally unstable friend Jessica (Zohra Lampert). She rises from a lake in a wedding dress in what is perhaps her most memorable scene.

The youngest of three sisters, Mariclare Catherine Costello was born on Feb. 3, 1936, in Peoria, Illinois. Her mother, Margaret, was secretary to the Speaker of the Illinois House of Representatives in Peoria and Springfield, and her father, Dallas, was a civil engineer for the Illinois Department of Transportation.

Costello attended St. Mark School and the Academy of Our Lady in Peoria and went to the all-girls Clarke College in Dubuque, Iowa, spending time at the University of Vienna during her junior year.

She received her master’s in Theater and Education from Catholic University in Washington, where she studied improv with Viola Spolin and performed for President Kennedy as Nerissa in a production of The Merchant of Venice.

From hundreds of actors who auditioned, she was one of just 30 in 1964 to be selected for the original Lincoln Center Repertory Company, led by Herbert Blau and Jules Irving. That year, she originated the role of Louise for Elia Kazan in Arthur Miller’s After the Fall, starring Jason Robards and Barbara Loden.

Costello also worked at the Sheridan Square Theater and The Public Theater and made her Broadway debut in 1965 alongside Stacy Keach in a revival of The Country Wife, followed by 1968’s Lovers and Other Strangers, 1969’s A Patriot for Me and then Harvey, where she played the psychiatric hospital nurse Ruth.

Along the way, she trained with and worked opposite the likes of Jerome Robbins, James Earl Jones, José Quintero, Hal Holbrook, Austin Pendleton and Faye Dunaway.

While still attached to The Waltons, Costello recurred on the 1976 CBS drama Sara, which starred Brenda Vaccaro as a teacher in a one-room Colorado schoolhouse in the 1870s (it was canceled after 12 episodes).

Her résumé also included the films Ordinary People (1980) and The Adventures of Buckaroo Banzai Across the 8th Dimension (1984), the 1976 NBC miniseries Raid on Entebbe (her husband was in that, too) and TV stints on Ironside, Kojak, Harry O, Lou Grant, Murder, She Wrote, Chicago Hope, Judging Amy and Providence.

She and Arbus first met in an acting class taught by Mira Rostova, and they fell for each other while in rehearsal for the Dorothy Parker one-act play Here We Are. They moved to Los Angeles in the late 1960s and married in their home after 12 years together.

Costello led the drama program at St. Paul the Apostle Elementary School in Westwood and directed plays at Loyola High School and Loyola Marymount University, where she also taught acting for many years.

She also directed productions for Interact Theater and led a theater group at Homeboy Industries, the gang rehabilitation and re-entry program. Her basement was filled “floor to ceiling with costumes and props, and her productions were works of extraordinary care and beauty,” her family said.

They added: “She was also, in every dimension of her life, someone who paid attention. She could talk to anyone, was interested in everything and was a relentless asker of questions. She loved stray animals, rescued bugs, fed birds and knew that few pleasures in life rivaled a good curbside furniture find. She was a wonderful cook and wrapped presents with the kind of care that made the unwrapping its own event. She refinished countless floors and collected objects, letters, photographs, even used coffee cups, much to her husband and daughter’s dismay. She made every space she inhabited more beautiful. Warm, curious, generous and tough, she had the constitution of an ox, was never sick and was always up for an adventure, especially if she could show up a few minutes late, as was her general inclination.”

Survivors include her daughter Arin and her partner, Ethan; granddaughter Bird; step-daughters Amy and Doon; nieces Moira, Elizabeth, Molly, Sarah, Kate and Julia; and nephew Jim.

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