Looking for the silver lining... At least your mom was holding credit cards instead of reading the account number off a blank check. If they had taken money from credit cards, you have recourse through the card issuer to dispute the charge. If they got her to transfer it out of her bank account, it's gone forever. I know from personal experience that elderly people like to use cash and checks. It's a good idea to try to get them used to paying everything with a credit card and then writing one check a month to pay the credit card off. With the way such fraud is getting prevalent, I don't expect that credit card issuers will be able to remove disputed charges as readily as they do now in the future, but for the time being at least, it's the safest way to go.
In any case, I'm glad you showed up in time to avert crisis.