Amex Question

Got a different type of question. My mom had a stroke a little over a month ago. She's fine and recovering, but still can't fully communicate. I'm a signer on her checking account, and have taken over her finances in the interim. Well, she has an Amex card that has a balance. The account had a payment due a few days after her stroke. I didn't find the bill until it was already late. I called them to explain the situation and to see if they would waive the late feel. They wouldn't and wouldn't give me any info on the account, understandably since I'm not on it.

Well, I get this month's bill and because last month's was late, she's incurred the penalty interest rate of 29.99%, up from 13.99%. The new rate only applies to new purchases, which there shouldn't be any except for a few recurring bills she has set up on it.

I don't have power of attorney, as we didn't feel it was needed. Should I get one just to take care of this one thing? Is there another way I could get this corrected? Doctors are confident she'll regain her communication and she can maybe handle, but I'd rather do something now if I could. I found all of her old statements and she's never been late on this card, and I hate the feeling that I'm somewhat responsible though it was a bit out of my control.