Everyone's birds with larger combs and wattles are dealing with frostbite this year.  I'm not sure why that is.  I have never had frostbite in my flock, but this year my roo has it on his wattles from dipping them in the waterer.  You can go one of 3 routes for dealing with frostbite:
1.  Treat it with straight betadine twice a day until healed.  This will help dry out the bite and get any necrotic areas to slough off more quickly.
2.  Treat with Neosporin as needed.  This prevents it from happening again by applying an ointment, but takes longer to heal.
3.  Don't treat it and just monitor it for signs of infection.
I am taking option #3 with my roo because his case is so mild and only on one wattle edge, so I have been watching him and when it first happened I treated it, but he gets so annoyed about me fussing over him that I stopped to save the peace. 
Only you can judge how severe the frostbite is to your BO, so you will need to decide if she needs treatment or not by your own observations.
Good luck.