It looks to me like she may have had feathers picked by another. Get some BluKote from your feed store to spray on her bald spot to help prevent pecking. Some people use BagBalm, Vicks, arthritis ointment containing menthol, and anti-pick lotions instead.BluKote has worked for me. Make sure that you ens are getting plenty of protein in their diet. A good commercial layer or all flock feed is best, with avoiding overcrowding and boredom, to help prevent feather picking. Look for lice or mites around the skin under her vent just in case that may be a problem.