I'm sure the vitamins will help, try to keep her dry exspecially since you have had a lot of rain. I don't believe she has anything contagious or diseases that is why, I asked as far as treating her with Cocci. Like I said moving from one place to another can really put a lot of stress on a chicken.
I would still keep her separated but in a spot to where the other chickens can see her but can't hurt her. I would put her into a dog cage or something so the others can come up to the cage to check her out but she can easily back away when she feels threatned..When you introduce a new chicken into a new group, there's always risks unless you keep them separated and gradually introduce them with each other. I'm sure she will be fine in a few days or so. But I would not keep her with the others until she fully recovers and then slowly introduce her to the gang.