Aahh ok, so this is the hen you're hoping will go broody. Don't let her. It will not be good for her. I would probably give her some wet mash a fee times a day to get her to eat some more (and it will also provide water to help her not get dehydrated) and just watch to make sure no others are...
I agree. This doesnt look life threatening. The comb could be from pecking (chickens do this because of. Bullying, too small of a coop, boredom, or they might have seen something on her comb and tried to get it) or frostbite (not life threatening)
Are there any other symptoms OP? How old is...