Vaseline is said to be a good preventative for frostbite but I don't think it will fix it after the damage is done because the healthy cells have been destroyed. Assuming frostbite is the same in humans as well as animals what has happened is the water in the cells freezes and expands tearing...
Yep that looks like frostbite. I don't know how to help after the fact but I have read several times here on byc that coating their combs with Vaseline will prevent the combs from freezing.
Sorry about your girl. Hopefully you will find more helpful info
First
Second, I really don't know what is wrong with your chicken but the first thing that came to my mind was frost bite. What state or country do you live in? Is it really cold there?
Maybe someone else will chime in with some wiser words than I have. You wouldn't happen to have a...