It's normal for a wound to be warm. Hot, red, swollen, and with red streaking in the direction of the heart is always a bad thing, though. If you want to try to amputate the foot to save her, it might not hurt to give her antibiotics. I would clean the leg area very well before removing the...
I would cull the hen, too...but the I think the wrap sweetxlilac was thinking about is Coban. It is usually tan if you get if from a drugstore, or in bright colors at the feed store.