Not an emergency, but Henrietta, my barred rock hen, has bare patches on her chest and on the arch (top) of her wings, where the feathers are broken off or missing. We sprayed SEVIN in the coop, changed all the shavings in the bottom, put Frontline on all the hens, and sprinkled their dust bath area with SEVIN powder. 3 weeks later, it is worse than before. She is not being picked on by the other hens, and she is healthy and laying well. They free range for 10-12 hours per day. Any hints, suggestions, or answers? Thanks!