My first suspect in cases of fur loss and/or excessive grooming is always diet. You say you haven't changed her food in years, but most allergies come about from repeat exposure to the same ingredients (typically inferior ones like grains or highly rendered meat, such as would be found in most dry foods). What exactly does she eat?
A vet visit is a good place to start for sure, although I have to warn you that most conventional vets just tend to throw steroids or antibiotics or crappy prescription diets at the problem without really looking at the WHOLE cat. Having said that, if your kitty hasn't had a thorough check-up recently, with blood work and a urinalysis, that might be a good idea. Then depending on what she eats, I think a diet change to a high quality, meat-based, grain-free, fish-free WET food, perhaps with a novel protein source like venison or rabbit, could really help.
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler