I think that this is either ringworm or another fungal infection. I think. Now is when you call her vet, or find her a vet, and have that looked at. In the mean time, to keep her a bit happier, you can purchase plain, unblended chamomile tea bags from the grocery store. Brew a cup, and chill it in the fridge. When it is nice and cold, apply it to the "rashy" areas with a soft cloth or a cotton ball. Chilled chamomile tea is wonderfully soothing for skin ouchies on almost any living creature, and since it is safe for cats to take internally (for mild anxiety), it won't hurt her one bit if she grooms it. You can use it several times a day. It is mildly antibiotic and antifungal. Although I doubt it is strong enough to clear whatever that is up, it may help keep it from getting worse until her appointment.
Did the shelter give her medicine for fleas ? she may have had an allergic reaction to it. It looks like possibly contact dermatitis ..an allergic reaction . Best to get to vet asap. If that is the case, you would need to know so she isn't given the medicine again. Hope your new baby is feeling better !!
It could be a healing wound too, those areas often lose their fur. It takes a LONG time for it to grow back. I think it is too low on the back to be from flea medication and is not ringworm, it would have spread by now, and to you. Those lesions are usually smaller and round. I don't see the circular areas indicating ringworm. You could get some cat wound spray and spray it on a rag and apply it, cats hate the spraying sound. Then maybe some antibiotic salve without pain killers in it.
you are right .. flea medicine is usually closer to the neck area . it looked closer in the pic, but when I looked again, it didn't look as close. I think you are right...
I put flea meds really high up. Almost start between the ears. One time I got it too low, the cat turned enough to lick it and ran around like crazy, foaming at the mouth. It didn't hurt her but it was scary!