Could she have done this to herself or could there be another cause?

This is a new bald spot that is about the size of a quarter on the base of her neck. She should not be able to reach this spot with her mouth and I don't know whether it's possible she did this by scratching herself.

She was left with family while I was away on a trip. She did not have a collar on during that time and she was in her own room the whole time because she doesn't get along with the other cat. (She had food and water and her own litter box and the family was supposed to check in on her at least 2 twice a day.)