I used to travel about 70 miles each way to visit my old dentist when we moved house - the practice didn't mind at all, and were very helpful. I was lucky in one way as the dentist decided to not do NHS patients any more (he was nearing retirement age) and I rang the NHS to find out about dental practices near Portsmouth, where I now live, and found out that there was a new NHS practice opening about 3 miles away from me! We got on the waiting list very quickly, and are pleased with the treatment we have received. I think it's worth giving the NHS a ring just to see if there are any new ones opening near your mother. Anyway, good luck to your mum!