Exactly which part of the chicken is bald? Is it her crop, which is located at the bottom front of her right breast, or is it back near her vent, on her bottom? Has she lost weight? Feel her keel (breastbone) and see if it feels sharp to your hand. Also check her over for mites--tiny, pinpoint-sized external parasites. Signs of mites include a grayish dust-like material at the base of the feather shafts, most commonly on the 'fluffy' areas--near the vent and on her undercarriage. If she has mites, you need to treat for them ASAP, as a bad mite infestation can so weaken a bird as to be fatal. Any other symptoms, such as odd poop, not eating or drinking, looking listless or sitting fluffed up with her eyes closed, etc?

More help is on my chicken info site here, this is the page on health which might be of help with diagnosing her and supportive therapy tips:

http://jackshenhouse.com/VSChickHealth.htm

Velvet ~:>