Correct me if I'm wrong, but isn't that her breast and abdomen in the pics? If she is molting, you would see feather loss in more parts of her body. I would dust her with poultry dust for mites. I would also watch to see if she is spending extra time in the nest box. Some hens that are building a nest to start to brood pull breast feathers out to line the nest.
This was my thought too, that she is broody.
So glad you found her, and in the nest box too!
He still wants me to get some royal palm hennies. Yup, as much as he won't admit it, he's a convert!