Peabody was born on January 11, 1948 in Portland, Oregon, though she grew up in Miami, Florida where she pursued acting at a very young age. In the mid 1960s, Peabody made her debut appearance in the educational film that delved into drug abuse called Misfits. The film was produced by a company in the New York area and she got the part after one of the actresses was unable to commit to filming after becoming sick with an ailment. In the early 1970s, she was mostly cast in low-budget drive-in films that were being shot in Florida such as The Horse Killer (1970), which Peabody stated, “It was actually based on the true story of a man who castrated horses! It was a really bizarre story, but it wasn’t like Last House, with sex or murder. It was more of a mystery, where these incidents were happening and they were trying to find this weird guy who was doing it. I was playing the girlfriend, and we had a lot of scenes riding horses and that sort of thing.

In 1970, Peabody had a supporting role as The Sun in Robert Kalfin’s Off-Broadway production Tarot which ran at the Brooklyn Academy of Music. Additionally, she began to appear on television in commercials and on the two soap operas All My Children and As the World Turns in supporting roles.

In 1974, Peabody had a cameo role in the horror film Legacy of Satan. The following year, Sandra starred in the comedy film Teenage Hitchhikers, which was about a couple of young hitchhikers who embark on a cross country trip in search of freedom, excitement and independence. In a review for Los Angeles Times, Linda Gross stated that Peabody’s performance was “ingenious.”

After appearing in Teenage Hitchhikers, Sandra quit acting. In 1975, Peabody worked as the script supervisor for the exploitation film Video Vixens, in which she is credited for the script continuity and featured her Last House costar Steve Miner as the assistant editor.

Subsequently, Sandra began to distance herself from the exploitative films that she was becoming known for and began to transition into children’s programming. In 1983, she joined Mary Lee Fones and Karen Kalergis in an effort to bring child friendly content to cable systems beyond prominent film industry locations such as Los Angeles and New York. The same year, Peabody created the half-hour children’s program Get Moving. In 1990, Sandra wrote and produced the television series Where in the World. The series lasted until 1995. In 2000, David A. Szulkin interviewed Peabody for his book, Wes Craven’s Last House on the Left, which tells the inside story of making the film.

In 2001, Peabody wrote and produced the educational series Zone In. She created more entries in 2007. Peabody has appeared in several critically acclaimed horror film documentaries through archive footage such as Going to Pieces: The Rise and Fall of the Slasher Film (2006) and Never Sleep Again: The Elm Street Legacy (2010). Peabody was Alicia Lagano’s acting coach and in an interview stated:

Peabody was later cast in the horror films Voices of Desire (1972), and Massage Parlor Murders! (1973), the latter being a grindhouse film that was released on DVD and Blu-ray in 2013. Her next role was Olga in the satirical exploitation film The Filthiest Show in Town (1973).

In a 2016 editorial for the website Birth.Movies.Death., actress Barbara Crampton noted that Peabody was one of the first actresses to be labeled as a “scream queen” due to her frequent appearances in horror films, stating:

As of 2019, Peabody is reported to be an acting coach and agent in the Portland, Oregon and Los Angeles, California areas.