The California Department of Correction and Rehabilitation said that Susan Russo died of natural causes on Friday.
The age of Russo was 67.
According to a CDCR news release, Russo had been receiving medical treatment at a local medical facility since August 16.
She was found guilty of first degree murder and conspiracy in the death of David. He was a naval officer.
She wanted to collect benefits as her husband's surviving spouse, so she paid her boyfriend to kill him. She let her husband's killers into her home, where they shot and killed him.
He was admitted to the state prison in October of 1996 to serve life without the chance of parole.
She was sentenced to six years for soliciting someone else to commit or join in the commission of murder.
She was eligible for parole after former Governor Jerry Brown commuted her sentence.
Brown blocked her parole in January of last year. Brown said she had more work to do.
The woman had accused her husband of physical abuse. She wrote in her 2012 clemency petition that she was protecting herself and her children from an abusive husband and father.
After Brown commuted her sentence, the parole board investigated her claims of being battered by her husband.
The cause of death will be determined by the sheriff's office.
The AP contributed.