I've had TMJ for years, (sense I was 15 years old) and it has never gone away. However, mine wasn't caused by dentistry, so this may not be the case for your mother.
My advice is this: First of all, ibuprofen (Advil's main ingredient) has always worked as a pain reliever for my jaw. This is because ibuprofen is an anti-inflammatory agent, and helps relieve the tendon and muscles.
Secondly, press an ice pack, or a cooled wash cloth to the side of the jaw that hurts when it starts hurting. This will also help the inflammation that causes the pain that your mother is experiencing. If this does nothing, you could try a hot press of sorts, but it's never done anything for me.
Thirdly, physical therapy does exist to help people with TMJ. I went to a therapist who helped work my jaw and taught me many simple exercises to help relieve my TMJ pain. My favorite, and the most useful to me, is to press your tongue to the roof of your mouth, and, keeping your tongue pressed there, open your mouth 10 times. (not to the point that it hurts, but enough to stretch out those jaw muscles.) I made sure to do this three times a day. More if I needed it.
Anyway, I hope that this was helpful to you. You and your mother will be counted in my prayers.
Good luck, and God bless.