Xantham gum is a binder. Its used in the same way gluten is but I don't know about the other. I don't think it will hurt her. I think the vitamin d is there to help calcium absorption and the oregano is for respiratory health. I give my girls something similar when the weather is bad or they're...
Maybe they will get some answers that will help you. I have a Black Australorp with toes on both feet like yours has. Her name is Mama Toe and she's one of my favorite chickens ever so I'm rooting for Broken Toe to pull through!
Does she still lay eggs? Extra calcium if she's not laying eggs might not be a good idea although that elixir doesn't have much in it. I would keep soaking the flock raiser to make a mash and feeding her that. I would also have fresh water available in addition to the other. Her poop looks...