I trust yogurt, it even takes care of e-coli. Mountain High makes a great one, plain, unsweetened with several different types of probiotics. My birds love it. Any stress at all, and they get yogurt. I don't use antibiotics unless I'm absolutely forced to. The yogurt does a fantastic job and it sounds to me like your girl needs it! Is she out in the coop with your other birds? If you don't want to bring her into the house, you should provide a place for her out in the coop where she can be under some heat, where the other birds won't bully her away from it. If she doesn't have to keep herself warm, that's one less battle for her, perhaps she can concentrate on resting so she can get well.