According to Deadline, actress Sian Barbara Allen (L.A. Law, You’ll Like My Mother), known best for her role in the 1972 historical drama series The Waltons, passed away on March 31 in Chapel Hill, North Carolina. She was 78 years old. Her family confirmed that the cause of death was Alzheimer’s Disease.

Born on July 12, 1946, in Reading, Pennsylvania, Allen was raised by her mother and grandmother. After graduating high school, she earned a scholarship to the Pasadena Playhouse, setting the stage for her career in acting. She later studied under the esteemed acting coach Peggy Feury (All of Me, Crimes of Passion) as part of a program at the Mark Taper Forum.

Via Deadline, Allen’s career took off in the 1970s when she became one of the last contract players at Universal Studios. She appeared in numerous hit television series of the era, including Hawaii Five-0, Columbo, Gunsmoke, The Rockford Files, and many more.

On the big screen, Allen starred in the 1972 thriller You’ll Like My Mother, sharing the screen with actors Patty Duke (The Miracle Worker, Captains & The Kings) and Richard Thomas (The Waltons, It). This performance earned her a Golden Globe nomination for Most Promising Newcomer.

Allen was often cast in roles that allowed her to bring a deep sense of “great vulnerability and uncommon empathy, which won her a legion of fans all over the world,” according to her obituary.

Deadline stated that beyond television and film she also had a passion for theater. One of her most beloved roles was Emily Webb in Our Town, which was performed at the Williamstown Theatre Festival in 1976. In tribute to the character, she later named her daughter Emily.

After stepping away from the entertainment industry in 1990, Allen dedicated herself to political activism. She, along with her then-husband Peter Gelblum (Kojak) and daughter Emily, volunteered for Jackie Goldberg’s 1993 Los Angeles City Council campaign. A strong advocate for workers’ rights, she was a vocal supporter of Cesar Chavez and the United Farm Workers. As stated by Deadline, her family noted that she “never crossed a picket line in her entire life.”

According to Deadline, she is survived by her daughter, sisters, nephew, cousins, ex-husband, and grandson Arlo Fonseca.