I would have the dog checked out thoroughly by a vet first. If all is clear health wise then definitely go with training. It sounds like the dog's true personality is starting to emerge and he may be very dominant. We adopted our TM almost 10 months ago and his personality is still changing a little at a time. Your mom is going to have to establish her dominance over him and if she is not comfortable doing it may need some professional help. Our female Springer would bite when you brushed her hips (because it hurt) or if you tugged too hard on a tangle. Her skin was extremely tender for the last few years of her life. She would also growl and try to bite you if you rolled her onto her stomach, again because it hurt. Our Pyr will growl at my husband if he rolls him over in bed, but if he tells him to move, he will. It's kind of funny because he never growls at me no matter what I do. He thinks it is a game with my husband and wants to play if he is pushing him around physically.
If you encourage and coach her through it, she should do just fine. One of the first things she can try is making him earn everything he gets. For his food, he has to sit, stay, shake hands, down, something. Same thing for treats, petting, going outside, everything. Anything he wants from her he has to earn. That way he learns who is in charge. Good luck and I hope this is something she feels she can work through.
Kathy