Name change help

Location: California So I’m posting on here for my mom. She got married like 20 years ago to her bf who was in prison in a different city but still in Cali at the time. Got her name changed to his and everything. Fast forward, he filed for divorce while inside and has been married to someone else and is free. Her being smart decided since they were done she didn’t need the paperwork anymore so the problem is my mom never actually changed her last name back and now that she’s trying to, she can’t. She’s gone to the dmv, She’s gone to the court but they say they have no record of the divorce or the marriage in the city we’re in. She’s called the court in the city where the prison is since that’s where they got married and they said the same thing. It’s like at this point what can she do? Any help would be appreciated!