Legal Question in Real Estate Law in California

I suggest both of you make an appointment to meet with the decision-making loan officer at "her bank" to discuss what kind of proof would be satisfactory. At that time, you can propose the alternate methods of establishing that she is not liable on your loan and see what they'll accept. It could be that merely appearing in person and telling the loan officer, face-to-face, what the facts are will be sufficient. Or, perhaps you could show a copy of your mortgage statement without handing it over or permitting its copying. However, in the overall you may just have to give up your reluctance and provide the requested documentation. It seems rather unlikely to me that this would materially increase your risk of future credit-card fraud.