I saw a chicken for sale on here or Craigslist or something and it was missing a foot and seemed fine. I guess I would see if she gets around okay. She might have trouble getting onto the roosts or up a ramp is the only thing so you might have to make some modifications for her. But for a chicken, losing a foot is a bigger deal than say a dog or cat losing a leg because they're prey animals plus they only have 2 instead of 4 legs so balance is harder. Putting her down would probably be the kindest thing to do but if she appears to be eating, drinking, and moving around fine otherwise you could see what happens, if you're willing to make some modifications. I will say though that you can't just leave her, you need to check her foot and make sure there is no infection or injury and treat if there is. You also are going go have to make some modifications to your coop and/or your care/maintenance routine so no one else gets frostbite. And some handicap adaptions for her. People do keep handicap chickens, there's even some people with some blind chickens, so if you want, wait and see. But also remember that chickens tend to hide illness so she may be pretending there's no pain