I believe your mother would get justice if your facts are right. It is important that she act fast. Making a fraud charge is a serious matter. It is crucial to establish all the facts before making a firm position.
The burden is for the bank to establish it was your mother raised the loan, the loan released to her and many other factors. Some investigation would look at the trusting relationship of your mother with your step father; the bank dealing through your step father; and the cautions that proper legal advice was given to your mother.
I suppose you do not need to worry about the bankruptcy issue now. It is far and highly uncertain this stage will happen. The bank may not even going to sue your mother in court if the strength of your facts is good. There are many strong precedents in this area.
