Do her waddles feel hard or brittle at all? If you think it is frostbite you can put some vaseline on her comb and wattles...it won't heal anything that has happened so far, but will keep her from getting frostbit any worse. I have heard that frostbit combs will turn black, and my rooster has a few black tips on his comb some mornings, but I notice that they seem to color back up when the weather is warm...I should probably vaseline him up, but I haven't...it doesn't really get too cold here, but barely below freezing, so I figure it can't be too bad...if an area gets frost bitten severely the area will become necrotic, turn black and fall off...sometimes it can cause infections, but as I said my fellow gets a few black spots and then they are gone...I don't see what looks like frost bite on that hen though..but it sure does look swollen. I would keep an eye on it, and go ahead and vaseline it up and see if that helps at all.
