During the trial, Fromme was convicted of trying to prevent other "Family" members from testifying and of contempt of court for refusing to testify herself. She was given short jail terms.
The prosecutor who put Charles Manson behind bars 40 years ago said Fromme remained a danger and said she should not be released from prison.
"If you do something like that against the president of the United States, the need for deterrence increases when you're talking about the most important person," said, Vincent Bugliosi, the former Los Angeles County assistant district attorney.
"She was the main gal in the family. Once Manson left the ranch, if he was anywhere else she was in charge," Bugliosi said.
During her own incarceration for the Ford assassination attempt, Fromme attacked another inmate in 1979 with a claw hammer and was transferred out of the women's prison in Dublin, Calif.
In 1987, Fromme became so upset at the news that Manson had testicular cancer that she broke out of the Alderson Federal Prison Camp in West Virginia in an attempt to reach Manson. She was captured two days later.