She needs to go to the doctor and have the reason for her vertigo checked out. Most likely it will be nothing serious and will be treatable.
Some examples:
My grandmother had vertigo for twenty years, successfully treated with a daily pill, and eventually died from something totally unrelated at the age of 89.
My father has had vertigo due to Ménière’s Disease since he was in his fifties. He takes Meclizine and generally has no problem at all. He’s 84 now.
I have periodic bouts of vertigo due to Benign paroxysmal positional vertigo. It was treated with physical therapy. Although it comes back sometimes, I am not dying any faster than any of us dies. I just keep going one day at a time.
Instead of worrying about whether your grandmother is dying, perhaps you could help her decide to go to a doctor.