I would assume the bandage became too tight and has caused some tissue damage. Can she move her toes or bend her foot at all? I would begin soaking her foot in warm Epsom salts water once a day for 15 minutes, then drying the leg thoroughly. Paint some iodine or plain neosporin on the bumble foot scab only. Keep her on a clean towel or puppy pad in a dog crate for a couple of days until the scabs seals.
Her skin may slough off(peel) in places or she may possibly lose some toe tips and nails. It looks like she might keep the leg though. With severe frostbite cases the dead skin shrivels, turn black, and the dead part falls off in weeks.
Hopefully, she will regain some of the feeling in her leg and foot. Good luck eith her snd let us know what, happens.