Our bard rock hen lost all the feathers around her vent area... and area about 3 by 3 inches, totally bare. We have tried dusting her with powder from the local grange but the feathers do not want to grow back... it has been about a month now that she dtill has a bare bottom. Any idea on what caused this and how to get her to grow her feathers back? She seems normal acting and does not seem to bother her. We have 4 other hens and they do not bother her and are not picking at her. She is actually the dominant hen of the 5.