I am so sorry to hear about your mom, and She should know many of us here have similar experiences. RA can be so painful, and I can feel my swollen fingers ache as I sit here typing.
You ask several questions that, unfortunately, we are unable to answer. None of us here are medical doctors, and each person's RA is so different that even if we could answer, our advice would not be worth much because we have not examined your mom or know her medical history.
It is important to know that usually once function is lost almost nothing will bring it back. So it is often necessary to treat pain and at the same time prevent things from getting worse. Because of that, I suggest you go with her to her next rheumatologist appointment and let them know of her pain and discomfort.
Some people have used THC with good results ( I have not ); most others rely on prescription medications often prescribed by a pain specialist.
You ask about ways to stop things from getting worse. That can be done with biologic medications or disease-modifying medications (DEMARDS). Again her rheumatologist will be able to help guide the selection.
I wish you and your mom the very best. Please let us know how things are going. We will be very interested.