Fraudulent Credit Card Debt

My 88 y/o grandma (Alzeihmers) has credit card debt of over $5,600, made by her daughter without permission. I am her guardian, have attempted to work with the card company to repay this debt. Initially, was allowed a no interest plan for 12 mo. and was told that good payment habits would assure participating in that plan. They also agreed to drop past late charges and interest of over $500. Pay has been timely, but they didn't drop the $500. After 1 yr, they dropped her from program & interest was set at 23.99%. Have been on another program twice, for 6 months, but interest rate and minimum payment goes back up. She is on fixed income, 24 hour care, and can't afford to pay more than $60 per month toward this debt. I have provided her income/expense info to the company many times, but quit allowing her to be on the programs. We are being charged late charges monthly because she can't pay the full minimum amount. I've asked them to provide proof of the charges so I can seek legal action against the person who made the charges, but they cannot provide the info. They call me everday at home and at work. Is grandma stuck with this debt, what are my options?