If she is trying to sell it fast, she shoulld be asking fo a Deed in lieu if she is wanting to gain ownership back faster, and then sell it. to whom ever. Otherwise, she'll have to go through the long drawn out foreclosure proceedings.
She is just the mortgagor ( the bank). You are the owners with a promiss to pay..Seller is not able to circumvent the Law..Seek Professional legal advice.
This is just my attempt to understand your issue