Hi again, Alice.
I'm so glad you could give Hallie a loving home!
From your description, this red, bumpy looking sore on the back of her neck, might signify various conditions. She could have miliary dermatitis, which is usually caused by an allergy to fleas or other allergies. Here is more info:
It also could be ringworm, a fungal skin infection that is very contagious between cats and humans can get it from cats and vice-versa.
If you did use any topical flea treatment on her in this area, it could be an adverse reaction to that. Another possibility is a bite from an insect or spider or an eosinophilic granuloma.
I realize you wanted to wait until she was more settled in her new home, but this should be looked at by a vet in person, so you can get a definite diagnosis and treatment. She can have her annual exam at that time.
It might be easier to have a mobile vet or housecall vet come to YOU, and that would be easier and less stressful for her. You can look here, to see if there are any in your area:
I hope all will be well with Hallie! Please let me know how she's doing and what the vet's findings are. Thanks!
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