pain in the hands
I had trouble with the hand swelling and pain for a long time after GBS finally released its grip on me. Spent 8 months in rehab in hospital and remember the pain being so bad that I would put my hands on the cool metal bars on the side rails of the hospital bed trying to get relief. The only pain meds that I ever got was Motrin during the day and a Darvaset in the evening. This was over 20 years ago and I am sure that things have changed since then when it comes to pain management.
The swelling & pain went away when I was finally able to get the use on my hands back a little. The more I used my hands the less swelling and pain I had, even though it hurt bad in therapy. It is important for your mother to keep up with the therapy and to keep her joints and tendons loose in her hands as much as possible. So when the muscles start getting the signals to move from her nerves she will be able to move without pain. The pain of loosening her fingers up after they lock up will be much worse if she neglects moving.
This is just my opinion and, of course, she should listen to her therapist. I wish her the best.