If she has worn a collar, it could be an allergic reaction to that, otherwise, it could be a whole number of different things. If you have a good rapport with your vet, you could send them that pic and ask if they have some suggestions on what to use to try to treat it.
Here is a link to an article about various skin conditions in cats, which may or may not help you. But there is a section that lists all the things your vet might ask you when you talk to them about this spot, so you could probably use that list of questions to help you explain to them about what you do or do not know related to this place. Cat Skin Conditions: Dry Skin, Skin Allergies, Skin Cancer, Itchy Skin & More | PetMD