There are really two different thing that could be happening here. They are quite different. She might have ptosis but she might just have loosened skin due to aging. Loose skin due to aging is done through a blepharoplasty where basically the excess skin is removed. It is often couple with a temporal brow lift. Blepharoplasty is usually a cosmetic procedure. You can have a situation where there is much loose skin that it affects vision and insurance or Medicare will pay for it.
I have had a cosmetic blepharoplasty and temporal browlift. I coupled it with a facelift and it was a cosmetic procedure since it wasn't affecting my vision. The recovery was easy and I am glad I did it (4 years ago). I did have revision surgery within the first year after. They are careful not to remove too much skin. It is much easier to deal with needing to remove more skin enough skin rather than removing too much. The revision was very easy to do.
Ptosis is different. Ptosis is when the muscles around the upper eyelids weaken and they don't lift the upper eyelids properly. That is often age related. Ptosis can also cause the eyelid to sag enough to interfere with vision. Ptosis repair requires a different procedure to correct. I have a slight ptosis in one eye. Not bad enough yet to do anything about. I notice it myself but most people would not.
Anyway, not all doctors who can do a blepheroplasty can do a ptosis repair. So if that is what is needed be sure to see a doctor who can do one