This could be a reaction to stress, a food allergy she's developed late in life, or a symptom of a malabsorption disease. (Sometimes animals, not just cats, when they are not recieving the proper nutrients from their food, will begin to exhibit strange behaviors such as self-mutilation. Older cats are very prone to developing malabsorption problems which means that their intestines don't absorb the nutrients from their food well anymore.) Whichever the case, she should be seen by a vet. If it IS stress, the vet can prescribe something to help calm her down (not necessarily something invasive), if it's an allergy you can talk about what could be causing it and food switches, and if it's a malabsorption problem you'd want to address that RIGHT AWAY because if you let it go too long, she will be too far gone to save. My mother's cat recently passed away at 17 from complications stemming from a malabsorption problem she left go too long, so I know whereof I speak.