Hens get bald spots from stress and in-fighting. I'm sure you've heard of 'pecking order'. It's quite literal. Perhaps the two have suddenly decided to fight for top chicken, or perhaps there is predator nearby increasing their anxiety. The constant egg laying must be stressful as well. Look into ways to slow her egg laying. I've heard of a similar problem before. When a hen comes to realize none of the eggs are hatching, she lays more and more and fails to properly care for them. It is a nesting problem. Remove the eggs for now and let her grow comfy on an empty nest. See if her egg laying slows any. If it does, let her sit on one egg, continuously, remove the others. It might calm her. This is purely theoretical, based on a similar situation I observed.
My Hen Won't Sit On Her Eggs And The Rooster And Hen Have Bald Spots On Their Head Any Ideas To Help?
Chickens don't usually stay in pairs, he may be harassing her to mate. Her breed may not be one that is broody, (wanting to set) Get some more hens, or incubate the eggs in an incubator.
She may not be ready to sit. The rooster is just breeding her to much. You need to get more hens for the rooster to breed so he wont tare up her head.