I have a 9 month old Welsummer hen that decided that she just had to go into a full molt. Couldn't wait till spring. She had to molt when the temps are in the single digits so her 'mom' would worry about her keeping warm. Luckily she is the only one of a flock of 16 that is doing this. Still she looks pretty dopey with a single tail feather sticking out of her backside.
I've been adding "Rooster Booster" vitamins and probiotics to their water. I have also been generous with the high protein snacks, fruit and sunflower seeds.
I also have a B.O. rooster who is suffering from frost bite . Only one in the flock without the common sense to stick his little pin head under his wing at night so I know what you mean about the weather not being molt friendly right now. Your hen will stay warm. She is probably cuddling up with her flock mates at night. Our molty girl isn't showing any signs of stress. She is eating well and keeping up with the flock. Hopefully the weather will break soon. and it will be a little easier on everyone. There is a food called Feather Fixer you might want to put them on. Indeed, switching their feeds may be putting them off a bit. I did that once before it hit me that our flocks liked MFA (Missouri Farmers Association) food (crumbles also) over ADM layer food. I would definitely put them on whichever feed they liked the best and leave them on it.
Have you wormed your flock? I'm not sure if you should worm the molty girl but the others may require it if they are all acting a little off center.
Good luck. It's been a rough winter for us also. The week before Christmas it was over 60 degrees where we live. Now it's 16 and they are calling for 5 inches of snow tonight. So far I have had one hen go broody due to the mild December temperatures, one molt and a rooster with frostbite who will definitely be a little less endowed once he heals. Oh, and one hen with a mushy crop.
I mean, can't they do this stuff when the temperature is 75 degrees outside?