Can you work with an occupational therapist who helps in this area? That's what they do. I'll be your mother's insurance or Medicare would cover something if the doctor recommended it. There's also a catalog that carries a lot of aids like this - some of them are bogus cures but some of the devices might be useful. I can't think of the name of it but maybe another mama can think of it. It's Dr. Something. If no one can find it, PM me because I think my mother has it.
I'm not sure what she does for coffee or hot drinks, but some people use the Keurig-type coffee makers because it's a one-hand "lean on it" operation. Not cheap but it makes things manageable.
And would she consider a patented food-based product with clinical studies to reduce the inflammation and pain? The arthritis will still be there, but if she has less (or no) pain, that might be a huge help. I have dozens of friends who've had phenomenal results - I was just at a meeting with a woman who was starting to get the "claw" type hands and was told she'd be in a wheelchair by now, but she's in her 70s and incredibly active and pain-free. I'm sure the same could be done for your mom if she'd be open to some information.