Amputation is best done by a vet. If there was a lot of blood loss, it may be too late. I believe that sometimes ending suffering is the best when something like this happens.
Where is the leg partially detached? Can you try to get her to a vet this am? If her leg is partly detached, I think infection and abscess will more than likely happen. It might be best to put her down if her wounds are bad. Hens can get around if they lose part of a leg with frostbite, but I‘m...