Where are you located in the world and how old is this pullet/chick?
How cold were your temperatures oh say a month or so ago?
Looks like Frostbite to me, you may have seen her with toes/feet yesterday. She has horn coloring on her legs and probably did on the toes too. Frostbite usually turns dark, so at a glance, the toes may have looked perfectly fine for a long time.
It takes weeks and weeks/months for frostbitten toes to auto amputate. Looks like this is what has finally happened.
Doesn't look like fresh bites from an overnight toe eating session from a rat. The toes are healed up very well, nothing to indicate fresh wounds.
Read this article and look at the long thread (photos). This will be helpful. She's walking on her stumps and the may harden up o.k. but you may find that she needs to wrapped to help her get around better. Prosthetics, you can try, but I've seen most report they are fiddly and the bird actually gets around better with just wrapped stumps if necessary.
https://www.backyardchickens.com/ar...to-know-about-injury-care-and-recovery.78168/
https://www.backyardchickens.com/threads/matilda-is-going-to-lose-her-feet.1454933/
This one too. If you note, the initial post was in January. The latest update was just a few days ago. You're looking at 4(ish) months and toes are just now being lost. A lot depends on the severity of damage and how fast the body auto amputates.
https://www.backyardchickens.com/threads/frostbite-frozen-foot.1609875/page-3#post-27670052