Sian Barbara Allen, a onetime Universal contract player who appeared in the films Youll Like My Mother and Billy Two Hats and played a love interest of Richard Thomas John-Boy on The Waltons, died Monday. She was 78.

Allen died in Chapel Hill, North Carolina, after a battle with Alzheimers, her family announced. She often played characters with great vulnerability and uncommon empathy, they noted.

In telefilms, Allen starred with Bette Davis and Ted Bessell as the title character, a housekeeper in a mansion, in 1973s Scream, Pretty Peggy at ABC; with Claude Akins, John Savage and Patricia Neal in the 1975 tearjerker Eric at NBC; and with Anthony Hopkins and Cliff DeYoung in 1976s The Lindbergh Kidnapping Case, also at NBC (she played the wife of the famed aviator). Born on July 12, 1946, in Reading, Pennsylvania, Allen was raised by her mother, Ruth, and her grandmother, Etta.

After she graduated from Reading Senior High School, she accepted a scholarship to the Pasadena Playhouse and studied with acting teacher Peggy Feury as a member of the Journeyman program at the Mark Taper Forum in Los Angeles.

She first appeared onscreen in 1971 on episodes of OHara, U.S. Treasury; Alias Smith and Jones; and Gunsmoke.

As one of the last contract players at Universal, Allen made her movie debut as a mentally challenged, nonspeaking girl in Youll Like My Mother (1972), starring Patty Duke, Rosemary Murphy and Thomas; for that, she was nominated for a Golden Globe as most promising new actress. (Execs at Universal liked her for roles earmarked for Carrie Snodgress, who had left the studio.)

She then played an unhappy mail-order bride in the Western Billy Two Hats (1974), starring Gregory Peck and Desi Arnaz Jr. and directed by Ted Kotcheff.

In 1973, Allen reunited onscreen with Thomas for two episodes of CBS The Waltons on the shows first and second seasons. They two were described as being together back then, and he insisted she get the part of the optimistic Jenny Pendleton, a big fan of John-Boys writing.

Her rsum also included roles on Owen Marshall, Counselor at Law, The F.B.I., Bonanza, Columbo, Kojak, Marcus Welby, M.D., Ironside, The Rockford Files, The Incredible Hulk and Cagney Lacey.

For a 1978 episode of ABCs Baretta, she shared screenplay credit with series creator Stephen J. Cannell.

Allen left acting after a 1990 episode of NBCs L.A. Law and maintained an intense focus on politics, her family said. She volunteered for Jackie Goldbergs successful 1993 L.A. City Council campaign and was a staunch supporter of Cesar Chavez and the United Farm Workers, they noted.

She also was a remarkable poet and leaves behind boxes of writing that her family will be able to read for a very long time, they said.

Survivors include her daughter, Emily (she named her for the character she portrayed in Our Town at the Williamstown Theatre Festival in 1976); son-in-law Max; sisters Hannah and Meg; nephew Miles; grandson Arlo; and ex-husband Peter Gelblum, to whom she was married from 1979 until their 2001 divorce.

She spent her final year in North Carolina, and donations in her memory may be made to the AuthoraCare Collective Hospice of Burlington.