please can someone help me figure out what this is!

one of my chickens randomly looks like this today and is not eating. as of now they are in a separate slightly smaller coop area. I am worried I get deeply attached to my chickens and this is my favorite one I really don't want to lose her. I assume it's some kind of virus but other than isolating them and trying to find a medication I don't know what to do or how much time I have left. (yesterday she looked completely fine and was acting normal all of this is from today.)