I think 53 years was more than enough–and probably too long in her case.
I'm not going to get into whole "Manson thing" here but we've seen time and time again what a "charismatic leader" can do when it comes to influencing those that are easily influenced to do some against the law.
From what I've read she's always been remorseful and accepted her part of the crime.
And she's been well-behaved while in prison.
I don't think she a threat to society, while at the same time paying a heavy price for what she did.
Then you have the cases like...
Kenneth McDuff, the "Broomstick Killer" who killed 3 kids in 1966, but was granted parole and released in 1989. He subsequently started killing again.
Arthur Shawcross, the "Genesee River Killer" who killed and raped a young boy and girl in 1972, was allowed to plea bargain down to manslaughter and was released in 1987–and started killing again.
Then you have a lesser known guy, George Fitzsimmons, the "Karate Chop Killer", who karate chopped his parents to death in 1969, was released from a mental hospital 3 years later and went on to kill his aunt and uncle in 1973.
If Leslie Van Houten moved next door to me, I wouldn't fear her in the least.