Divorced Taxpayer paid Tax to Ex. Ex didn't pay IRS


I have a client who divorced her spouse. Paid the agreed portion to their joint tax bill to him. He never sent it in to the IRS. So of course they are still coming after her. What type of relief can I file for her? I am considering an innocent spouse relief request. She filed one years ago but got denied. I have a notarized letter from her ex-husband confirming she paid him her agreed portion and to contact him about the balance.

I did speak with an agent. She stated they don’t honor divorce decrees. Can anyone suggest another type of relief request/abatement?