Hi yef: It's good your mother has you to watch over things, you're a great daughter!! Do you know what your mothers calcium level is, and whether they did a ionized Ca (calcium) or total Ca test? Usually if you have high Ca they prefer the ionized test, but it might depend on the dr as well.
When both of these levels are high-consistently-usually after several readings, they lean towards a dx of hyperparathyroidism. Has she had a scan of her parathyroid? If not I would have that ordered before she considers surgery. There are quite a few problems one has to have before they will consider removing part or all of the parathyroid gland.
There is a thread on this site about a dr in Florida, but honestly I don't know if he is considered to be the best, if there is such a thing. If your mom could get to a hospital that does a sestimibi scan they could tell if there are any things growing on the gland or if it's malfunctioning.
I have hypercalcemia (of unknown origin) but my PTH is always normal, so they continue to rule out hyperparathyroid for that reason. Make sure she has an excellent dr in this area (Endo) before she proceeds and I hope they find out what's going on.
To find the thread for the Florida dr, type in hyperparathyroid in the search box above this post to the right. There are quite a few people who post here that have had surgery by this dr, so you could read their post's. This dr also has a website that you could read after you find the post's I'm referring to. The site does have a lot of good info, I just don't know much about his credentials. I'll let the others with first hand experience fill you in on what they think about this dr.
Good luck and keep us posted on this...