A U.S. federal judge on Thursday sentenced former Boston mob boss James "Whitey" Bulger's girlfriend to spend 21 additional months in prison for refusing to say if anyone helped the couple during their 16 years on the run.

Lawyers for Catherine Greig, 65, had said that punishment was too severe for a woman they described as an animal lover and model prison inmate who was never accused of joining in on Bulger's murder and mayhem.

Prosecutors had sought a sentence of three years and one month, while defense attorneys had argued six months would be more fitting.

Greig was arrested alongside Bulger in 2011 when federal agents caught up with the pair in a seaside condo in Santa Monica, California, where they were living with a cache of weapons and cash. Bulger fled Boston in 1995 after a tip from a corrupt FBI agent that arrest was imminent.

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Greig was sentenced to eight years in 2012 after pleading guilty to identity fraud and harboring a fugitive. Her sentence on contempt of court charges for refusing to testify will be added onto that time.

U.S. District Judge Dennis Saylor voiced no sympathy for Greig's apparent desire to show loyalty to Bulger.

"It is had to imagine being less worthy an object of love and affection than Bulger," Saylor told the court. "He is a lifelong criminal, not just a criminal but a murderer, not just a murderer but a serial murderer."

Bulger was on the FBI's "Ten Most Wanted" list for most of his time on the run and his story inspired multiple films, including 2015's "Black Mass."

Bulger, now 86, was convicted in 2013 of murdering or ordering the killings of 11 people. His months-long racketeering trial exposed his corrupt relationship with the Boston office of the FBI, which turned a blind eye to Bulger's Irish-American gang as it focused its energy on the Italian-American Mafia. He is currently serving two consecutive life sentences.

Greig's lawyers noted that her initial sentence was longer than the five years Bulger associate Kevin Weeks served for his role as an accessory to five murders.

Bulger claims to have paid agents for tips but provided no information in return.