I've found that once frostbite has actually killed the tissue, there's not too much you can do other than get them to a vet and get some antibiotics going to prevent infection.
If she's going to the vet on Wednesday, I'd just keep an eye on her and make sure the area around the part that's falling off doesn't look inflamed or infected or start bleeding. If you can, also make sure she's not rubbing it or scratching at it.
Cotton just lost one of his last frostbite scabs a month or so ago and the vet said that by that time if there's no infection, they have no feeling in those parts and usually don't even notice the loss.
Maybe someone else has some suggestions, though.