I'm glad what's on the comb is wiping off, it does happen from time to time, they get poop on them. Be thankful it wasn't across her back or something like that - yep, happened to one of mine one time, she needed a rinse LOL
When you get some help, soak the foot and gently wash off all the...
I'm sorry your hen is not well.
Where to start...let's look at the comb first. By any chance does that wash or rub off? For some reason that does not look like Fowl Pox to me, more it looks like urates - possibly she got pooped on? (it happens)
Now...when is the last time she laid an egg...