Are back of neck raw spots self inflicted?

My cat suddenly had a 1 inch spot between her shoulder blades that was totally raw and a bit scabbed. All the hair is gone just in this small area. Then a few days later there was a second one an inch over. She and the other cat in our home bully each other and chase each other somewhat. They sometimes may pull a bit of fur out with their claws if they tousle but this seems to me like lick marks from herself. Is this common?

She has over groomed her belly and legs in the past. We have never been quite sure if it is from stress or a dietary issue. We tried changing her food to a hypoallergenic one suggested by the vet who said usually this is an allergy issue, but it just doesn’t seem it is the simplest explanation. It hasn’t been possible to get a totally clean test of the new food because she always ends up eating a bit of her old food from the other cat’s bowl.

Is it common for cats to suddenly overgroom in this area? Any suggestions for how we can help her? I am thinking we may need to put both cats on the more expensive hypoallergenic food diet to get a real test to see if that is the problem vs stress.