So I have posted this past winter about my girls having some dirty behind issues. All are now good but one. Hers is still super gross and I have taken her in twice washed her off, had to cut some feathers off and put bag balm on her, and still she has a gross behind. I want to bring her back in the house, but she doesnt like being away from her sisters. Any suggestions? Could it be worms? Or winter stress?