In a surprise move, a California panel recommended parole for the youngest member of the Charles Manson killing cult, but the sister of victim Sharon Tate is doing whatever she can to block Leslie Van Houten's release, calling her a "monster."

"They are still sociopathic individuals and capable of great brutality," Debra Tate said on Good Morning American of Van Houten and other members of the Manson cult. "The heinous crimes that were committed in the past, in 1969, will repeat themselves again. I am quite sure."

Tate, 63, attended the five-hour hearing in Chino, California, that led to the recommendation that Van Houten, 66, be released on parole.

Members of the so-called Manson family were convicted of killing seven people in a bloody rampage over two nights. Film director Roman Polanski's wife, 26-year-old actress Sharon Tate, who was eight months pregnant at the time, was stabbed to death as she pleaded for her life. Four others visiting Tate in her Benedict Canyon home in southern California were also stabbed to death. The victims' blood was used to write words and messages on the wall, including: "Pigs."

Van Houten, who was 19 at the time, was not on the scene for the first night of killings but did participate in the equally brutal murders the following night of grocer Leno LaBianca and his wife, Rosemary. Daughter Cory LaBianca has also spoken out strongly against Van Houten's possible release.

Debra Tate has attended every parole hearing for every Manson family member since the murders. The panel recommend that Van Houten be freed on parole despite a life sentence because she has been a model prisoner and is sorry for her crimes.

Upon hearing the recommendation, Tate said: "Your heart sinks between your knees." She added: "It's absolutely mind-boggling what goes through your mind. All of the atrocities from the past, the brutalities all come flooding back."

These people are "domestic terrorists and when they're released they can go anywhere in the United States," said Tate, who has launched a petition against Van Houten's release.

The parole panel's recommendation will next go to an administrative review. The final decision will be up to California Governor Jerry Brown. In 2014 Brown rejected a recommendation to free Manson associate Bruce Davis, who did not participate in the two-day killing spree, but did kill two men, apparently inspired by Manson.

Manson, 81, remains behind bars serving several life sentences. None of his cult members has ever been granted parole.