With such a small foot and such rapid shrinkage I don't see it taking too long.
How is Rubber Band doing otherwise? Happy and healthy, or is RB depressed?
Dumb question but, does she have a name?
Does it look like she was owned and escaped? I've seen lots of pigeons escape at shows, they're usually banded too.
https://www.backyardchickens.com/threads/matilda-is-going-to-lose-her-feet.1454933/
The foot should fall off on its own. Amputations are ugly but i don't really see what y'all mean. This foot has all the right markers for an easy break away.