Oh, sigh, featherpicking....
No, alas, I never found a solution. It started with one girl and before you know it, all four were bare bootie monkey-butt chickens. Literally, it happened over the span of about 3 days. In February. When the temperatures were like -10F. It broke my heart. They stayed bare until they molted in the fall. That lasted about 3 months and then one went broody in December. She plucked her downy feathers again (I caught her doing it to herself), but the others have not followed suit. Yet.
Just for reference, my girls have AMPLE indoor space, so crowding was not the issue. They eat layer crumbles and get a daily handful of BOSS/corn for a treat. They live an extremely charmed life. Anyways, I have been extra aware this winter about limiting cracked corn.... they love it, but I thought that I could have overdone it last winter (in an attempt to keep them warm) and thrown off their nutritional balance. But alas, it happened again this winter. Feeding extra protein did nothing to encourage new feather growth. I put vaseline on their skin several times in the late winter as their skin got quite chapped. It looked sort of painful. I just had to wait until they molted. Very sad.
In no way did the lack of bootie down affect their lifestyle, health or laying ability. It just looked like I was an abusive mother. I had to get over it. Good training I guess for when my daughters hit their teen years.
Good luck hon!