A yellow scab on one of my hens— mites or infection?

[Tyranno-Chicken Rex]

Today I noticed a yellow scab on the belly of one of my hens and the area is pretty bald there too (although feathers are growing in). There are also bald spots under both wings, which makes me think it might be mites because I heard they like to stay under the wings? I didn’t see any directly however. I was also concerned it might be some kind of infection or illness. She seems healthy and none of the other hens are showing any scabs or other signs of infection or mites I think. The scab is at the bottom of the picture but please tell me if you need a better one.