Oh my goodness, I went through that, too, the first year I had my chickens. They say that chickens don't need heat in the winter....even in Alaska...but my little hen did! I would highly recommend taking her to a vet if you can. I wasn't sure what had happened to Amelia but she was limping badly one morning, and her feet were swollen. I couldn't tell if she had an infection first and frostbite second due to the infection or the other way around. I was terribly worried she was suffering and would die, so I called a parrot vet. Although they misquoted me much lower than the actual office call cost, in the end my piece of mind was worth it. They gave her antibiotics and pain killers that stopped gangrene from setting in and assured me I did all that I could for her.
She did lose all her toes on one leg, and the top tips of toes on the other, but the "palms' are still there. They dropped off without incident and minimal bleeding. She did not ever complain of pain through all of it. And I am happy to report, she is able to get around and doing well after building her a handicap ramp and perch. She is a reliable layer and a darling. Her gate is a little uneven, but she keeps up with the rest and it's been 4 years since the incident.
I realize your girl has lost more of the leg than the just the foot, which may affect her ability to move later and her ability to take the weight off the other now in order to heal. With the seriousness of her injury, gangrene is a big risk. I did try other remedies listed on this forum for the first 12 hours, but then realized it was way worse than could be handled without prescription medications unless I wanted to put her down and even that I knew I could not do on my own. Some of the remedies I researched would have actually caused more harm. She was a $2.67 chickie that I paid $162 for vet care. I don't regret it.
So far, I treat everything else on my own using this forum with much success. However, I do not believe I would have had such a good result without the vet.....and I think she would have suffered unnecessarily. If she is important to you and you think she stands any chance, don't wait!
(My coop was insulated and dry at the time and no one else had frostbite. I live in NW Pennsylvania. I don't know how and why it happened. I just know it is NEVER going to happen to me or my flock again. I use a SWEETER HEATER now no matter what the weatherman says. It costs very little compared to the pain I caused through my ignorance/innocence.)