It sounds like flea dermatitis but you won't know for sure unless you visit the Vet. I sounds serious enough and has gone on long enough you will likely need medications for her to stop the itching before she wounds herself and the open skin gets infection, and to get rid of the fleas. Please do not dose her again with flea meds. on your own. Even though the treatment you used appears not to have worked there is still the danger of overloading your cats system with doubles of flea med.
Actually, since you don't see fleas but she is still having extreme itching it has gone too far. Hope she recovers OK and gets the fur back. Fleas are worse in the early fall so it will not likely go away on it's own.