Hi Anne! Welcome to JustAnswer. I am a licensed veterinarian and I'm happy to be of help. Pimply dermatitis could be mange, could be bacterial, could be hormonally caused, or could be caused by all three.
I'd recommend that she have a skin scraping done (which can be done in the veterinary clinic), have her thyroid tested, and then treat according to the results of those tests.
Also, I really doubt that her problem is allergic, and if Niccolina is eating a high quality food, probably not dietary.
Hope this discussion has been helpful! Please let me know if you have more questions or concerns. . .Dr. Barbara