Frostbite from blizzard
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To prevent further frostbite, rub their combs with vaseline
Unless you have very large single combed birds like Leghorn the hens should not get frostbite. Your coop is lacking enough ventilation. In the cold north, a few climate zones colder, only my cock birds get a touch of frost on tips. I raise Plymouth Rocks which is a medium single comb breed.
They just need a tad more ventilation that's all. A hole saw and drill make short work of it. If a slanted roof then few holes on low end and few on high end under the roof over hangs. If a gable roof then few holes on each overhang end and few on each gable peak ends. Cover holes with hardware cloth. It doesn't take much to add ventilation. 2' hole saws are nice. If you don't ow one then large wood drill bits work too.
Do the open windows draft on them? There is a reason for the frost bite. I'd look to ending it. A well vented coop does not need fans. it's self vacuum and pumping out via convection.
A small nip of frostbite on tips wont hurt them. There may be some discomfort for few days but it ends and isn't much of a bother. Vasiline is a method to prevent it in first place and only used on the large combed cock birds in the North. It's a loosing battle up here and my boys loose half their tips. Pullets and hens don't even get a nip of it in well ventilated draft free coop.