Vaseline is said to be a good preventative for frostbite but I don't think it will fix it after the damage is done because the healthy cells have been destroyed. Assuming frostbite is the same in humans as well as animals what has happened is the water in the cells freezes and expands tearing apart the cell membranes. When it warms back up in humans it is quite painful because the nerves are firing all over the place. Black frostbite in humans more often than not results in amputation which leads me to think that she will loose her comb but could quite possibly make a complete recovery if infection does not take over. I would definitely get her out of the weather. Possibly in an animal crate/carrier in the house or barn or garage or whatever so that her body can start trying to heal.