Sian Barbara Allen was born Barbara Susan Levey in Reading, Pennsylvania, on July 12, 1946. She later adopted her stepfather's surname (Pokrass). She had two sisters. She studied at the Pasadena Playhouse from 1964 to 1965. Her performance as the mentally challenged Kathleen in Ausgeliefert (1972), opposite Patty Duke, Rosemary Murphy, and Richard Thomas, earned her a 1973 Golden Globe nomination for "Most Promising New Actress".
While working on 'You'll Like My Mother,' Allen met and fell in love with the man playing her character's psychopathic brother, actor Richard Thomas. The two began a relationship that lasted for several years in the 1970s. Thomas went on to play John-Boy on the hit TV show Die Waltons (1972). When the writers of "The Waltons" wanted to do a love story for John-Boy in the first season, Thomas suggested that his real-life girlfriend play his onscreen love interest. Allen appeared as Jenny Pendleton in the episode The Love Story (1973), which earned Thomas his Emmy award in 1973, and in The Thanksgiving Story (1973).
Allen portrayed the titular character Peggy Johns in the 1973 TV movie Scream, Pretty Peggy (1973), with Bette Davis and Ted Bessell. Allen worked steadily as a TV actress throughout the 1970s, appearing on such shows as Detektiv Rockford - Anruf genügt (1974), Der Chef (1967), Bonanza (1959), Rauchende Colts (1955), and many others. She also wrote a script for an episode of the fourth season of Baretta (1975). Her last onscreen role was in the L.A. Law: Staranwälte, Tricks, Prozesse (1986) episode Whatever Happened to Hannah? (1990).
Allen ended her acting career after marrying and giving birth to a daughter. She later channeled her creativity into writing. She was the older sister of flash-fiction author, editor, and teacher Meg Pokrass.
Allen died in 2025, aged 78, after a long battle with Alzheimer's disease.
