X-wifes credit card debt

My husband got a divorce from his first wife 13 years ago. She was awarded two debts to take care of and my husband got all the rest. One of her debts was a Visa card through the credit union which she said she took my husbands name of. 13 years later she's decided she doesn't have to pay on the credit card (which she's been the only one using it since the divorce) We received no notification from the credit union that the payment was not being made until it was reported to the credit companies as 60 days past due. We paid her up on the card and told her to take care of it. We stopped the card from any future use since we are being held responsible for the bill. She now has sent the credit union a cease and decist order stating that she is on a fixed income therefore she no longer has to pay the bill. Which now they want the money from us. What legal rights to be have? It says in the divorce decree that this was her bill.