Sorry to hear about what your mom is going through. That's terrible. But it sounds like she has tried only one set of splints? Most people who find relief from TMJ problems, have had to try at least a few different types of splints before finding something that really worked. Don't give up after only one try!
Years ago, I started to get pain and clicking in my TMJs. I tried all kinds of over-the-counter splints, but none of those helped. Then one orthodontist tried a couple different kinds of splints, and those made things worse. My current dentist has been a godsend: During the day I wear a regular splint, and at night I wear a splint called a Bionator, which keeps my top and bottom jaws in alignment, moves the lower jaw forward, opens up the TMJ's, and also prevents me from grinding my molars. Now I have no pain or clicking in my TMJs. I wish I had started the splint therapy decades ago!