Van Houten will be eligible for another parole hearing in five years.
"I know I did something that is unforgiveable, but I can create a world where I make amends," Van Houten said. "I'm trying to be someone who lives a life for healing rather than destruction."
The panel was also heard from relatives of the victims who were starkly opposed to her parole.
Van Houten was convicted of murder and conspiracy for her role in the slayings of wealthy Los Angeles grocers Leno and Rosemary La Bianca. They were stabbed to death in August 1969, one night after Manson's followers killed actress Sharon Tate and four others.
Van Houten did not participate in the Tate killings but went along the next night when the La Biancas were slain in their home. During the penalty phase of her trial she confessed to joining in stabbing Mrs. La Bianca after she was dead.
With survivors of the LaBiancas sitting behind her at the California Institution for Women, Van Houten acknowledged participating in the killings ordered by Manson.
"He could never have done what he did without people like me," said Van Houten, who has been in custody for 44 years.
After years of therapy and self-examination, she said, she realizes that what she did was "like a pebble falling in a pond which affected so many people."
"Mr. and Mrs. La Bianca died the worst possible deaths a human being can," she said.
Arguing to the board, Los Angeles County Deputy District Attorney Patrick Sequiera said some crimes may be an exception to the law guaranteeing the possibility of parole.
"There are certain crimes that are so heinous, so atrocious, so horrible that it should cause denial of parole," he said, elaborating on Van Houten's contradictions over the years.
In response, Van Houten's lawyer, Michael Satris, said his client "sank to the depths of Dante's inferno and she put herself there by consorting with the devil himself, Charles Manson."
However, Satris said his client has totally reformed herself.
"Leslie committed a great sin, a great crime in 1969, and in that time (in prison) she has developed into the equal of a saint," he said. "Everything she does is for humanity."
Van Houten was portrayed at trial by her defense lawyers as the youngest and least culpable of those convicted with Manson, a young woman from a good family who had been a homecoming princess and showed promise until she became involved with drugs and was recruited into Manson's murderous cult.
Now deeply wrinkled with long gray hair tied back in a ponytail, Van Houten at times seemed near tears but did not break down at the Wednesday hearing.
She said that when she heard the Manson family had killed Tate and others, she felt left out and asked to go along the second night.
Asked if she would have done the same had children been involved, she answered, "I can't say I wouldn't have done that. I'd like to say I wouldn't, but I don't know."
Asked to explain her actions, she said, "I feel that at that point I had really lost my humanity and I can't know how far I would have gone. I had no regard for life and no measurement of my limitations."
Van Houten has previously been commended for her work helping elderly women inmates at the California Institution for Women. She earned two college degrees while in custody.
Other members of Manson's murderous "family" have lost bids for parole.
One former follower, Bruce Davis, actually was approved for parole last year only to have Gov. Jerry Brown veto the plan in March, saying he wanted the 70-year-old Davis to reveal more details about the killings of a stunt man and a musician. Davis was not involved in the slayings of actress Sharon Tate and six others.
Van Houten and others were given death sentences that were later reduced to life in prison with the possibility of parole when the death penalty was briefly outlawed in the 1970s.
Manson, now 78, has stopped coming to parole hearings, sending word that prison is his home and he wants to stay there.