What is a banks liability if the papers on a mortgage were forged?

If you can prove the forgery, you could potentially void or undo the mortgage, because the mortgage  could not have been granted without your consent, if you were as you indicate, on the deed; if you can do this, the bank would not be liable for anything else (any other compensation), since the bank is not liable for another person's forgery: your recourse would be to undo the transaction. You can also sue the person who forged your name, though if that was your mother, you could only sue her estate if the period to assert claims against it is still open. 
However, at 10 years since the mortgage, you are well past your state's statute of limitations for fraud, theft, and breach of contract, which are the potential legal grounds for action in this case. That could prevent you from taking action even if you have a good case. Your state, however, follows what's called the "discovery rule," which means that the statutory period is extended if you did not and reasonably could not have known of the illegal action at first; it is extended until when you did or reasonably would be expected to have learned of that. That could extend the time you have to take action, *but* if you learned of the reverse mortgage 10 years ago, as your question seems to imply, then it is too late: once you heard about the mortgage, the law would expect you *then* to look into any illegality--that's when you should have discovered it. 
So there are several different issues present; you are strongly advised to immediately consult with an attorney, before any more time goes by.