It could be food allergis, flea allergies, environmental allergies, she could be making excessive cortical steroids herself in the system, move damage to injury to the dried skin. You will need to work with a vet to figure it out, your best bet may be a second opinion and possibly being treated at either a small animal teaching hospital or a strictly cat clinic because they see more specific cat issues than an all pet clinics usually does the steroid wrked.p for a few weeks chances are it’s either food or environmental but there’s no way to tell for sure.
If you let your cat play outside limit her exposure to an open grassy area, keep her out of flowers and bushes etc. do not let her run free because your neighbors may not be using pet safe chemicals on their lawns or in their gardens, The cat may be having allergic reaction to that issue if you allow her to wander.
Another item would be any flea collars, powders, flea applications on her or in your carpet. Other things that may trigger this kind of reaction could be carpet fresheners you use, carpet shampoos, new carpet that she may have allergies to, if you have changed your laundry soap recently, fabric softener, different soap shampoo your floors, new air filters, incense or candles, oil warmers all can add to pet allergies. If you have indoor plants or have purchased new cat furniture, changed litters or any products you have been using for, on the cat or even the house can make a change in the cat. This is not the complete list, you may find one on line that’s more detailed of what to check for.
Other ideas is internal parasites, some you cannot see in the litter box, they are close to being microscopic and live in the digestive tract, just another idea of what may be bothering the cat.
We have had similar problems over the years with our cats from scratching themselves bloody, over grooming and chewing themselves to relieve the itching. We kept a journal of who did what and where they spent their time for the day. We also logged what time if day we noted them scratching or licking the most.
Our long hair ended up being clipped short, he needed to regrow his coat but we had to make sure we brushed him daily to avoid the under growth from matting and pulling his skin so hard, once the excessive under hair was pulled his full coat it came back and he stopped biting at himself constantly. All the sprays and powders that we were told to use to prevent matting and that would loosen dead hair up to brush out easily were the culprits for drying out his skin and making himself chew himself raw, the perfumes they used to make the product smell good and the oils reacted against his skin when he was allergy tested.
Good luck with your search, it may be found right way what the problem is or it may take several weeks of trying. It’s frustrating at st it there has been sine change in the cats life, unless he’s not that old and just matured from kitten to cat then it more than lowly is a hormonal issue, let your vet help sort it out what the exact issue is,