Unless she is being killed, I would not move her from the flock as it causes so many problems when you want to put her back. If she is seriously getting picked on, try putting up some blind spots in your run, where a bird can get out of sight from the others. They tend to look terrible if they get a hard molt, but almost always, those feathers grow in fast. And in a week she will look much younger, shinier and healthier with the pretty new feathers.
I don't believe in yogurt for birds, but I would give a little meat. Maybe some deer scraps if your family is hunting. But really any of the higher protein bird rations would be good.
Mrs K