Once frostbite has occurred, touching or trying to rub something onto the damaged tissue will further damage it. The only thing you can do, and must do, is not to let her be exposed to more freezing temps. Once tissue has been frost bitten, it is even more vulnerable to further frostbite.
Freezing temps plus poor ventilation set up conditions where the water vapor at night from the chickens breath condenses on large combs and freezes. The solution is to create ventilation high up in the coop while leaving a door open at a lower level so convection can carry that water vapor up and out of the coop. You can also add just enough heat in the coop to keep it just above freezing, but do not add heat if you don't have that high-up ventilation as heat creates more water vapor and can make the situation even worse.
