Legal Question in Real Estate Law in California

it depends upon whta the loan modification papers state. If it is described as being a new loan and only she signs, he ex has no liability as he has not agreed to the loan. If it is merely the old loan with some terms modified, while the ex did not sign agreeing to the changes, he still technically is subject to the terms of the old loan although he might agrue there can not be two different contracts as to the same loan and that the bank has ended the first loan and replaced it with a new one.

A loan modification is not a refinancing. You need to read the papers, or have a lawyer do it for you. There are no "standard" terms for loan modifications. They can be as insignificant as a change in the payment due date from the 10th to the 15th of the month to as significant as creating a whole new set of terms and obligations bearing no resembalance to the original.