Ex has gone against divorce decree and let her house go into forclosure, is she responsible for paying the remainder of loan?

I'm going to answer this question from the debtor / creditor perspective, not from the marital / divorce perspective: As far as the bank is concerned, each of you is still on the hook for the entire amount of the mortgage loan. The bank was not a party to the divorce so the liability of each borrower to the bank was not affected by the divorce decree. If you had a lawyer representing you in the divorce this would probably be a good time to get back in touch. If not, you might want to talk to somebody who does that work as soon as possible. (Please note that I don't do marital work.)