Thank you for the info about Kitty.
The reason I was asking about location of the lesions is because fleas like to reside at the base of the tail, around the head and neck. I know you have not seen any and she doesn't go outside. It is good she already has a flea collar.
It sounds like her skin problem is seasonal, since it happened this winter and last, but not in the summer. When I hear about seasonal skin problems, it makes me suspicious of allergies. Animals do not exhibit allergies the same way humans do. Instead of sneezing, runny eyes and congestion, both dogs and cats can have itchy skin.
One thing I notice with cats or dogs with indoor allergies is that they get worse once the windows stay closed and the heat is turned on for the cool season. Cats can be allergic to dust mites, mold, storage mites, etc that are in everyone's house no matter how well you clean. The most common symptom is overgrooming or scratching. I've seen where cats will scratch so much their skin gets raw (like you noticed with Kitty) and they can even develop a skin infection.
There is a great article at www.veterinarypartner.com. Search under "Itching and allergy in cats" Just so you know, food allergies are less likely in a cat that only has skin problems during a certain time of year.
I recommend a visit to the veterinarian to see if there is a secondary skin infection due to the scratching. If so, she can be placed on an antibiotic. Also, there are medications that can relieve the itching short term. Many vets will use an injectable or oral steroid like prednisilone or methylprednisilone. It works to stop the itching quickly, but it is a bandaid. It will not eliminate the underlying allergy. The reason I mention this is if you do get steroids, use them sparingly. Frequent use can lead to diabetes, liver disease, and heart disease.
There is also a medication that has been used for cat allergies called Atopica. It is safer to use long term, but I usually only use it in an animal that has recurrent episodes.
If your vet determines there is an allergy, they may offer referral to a veterinary dermatologist for allergy testing and allergy injections. This is the most natural way to treat allergies.
Please let me know if you have any other questions or concerns. I am here to help.