My one note about worming is if you want to do it more consistently then you need to switch up what you use to worm. This is so the worms/parasites don't develop a resistance to it. I personally don't deworm mine and they don't have any issues. I will only worm if I need to.
Could the ventilation fan be introducing a draft accidentally? Also make sure there isn't any humidity as that can also increase the risk for frostbite.
There is no need to a heater in the coop and it tends to do more harm than good. If you keep a heater in the coop and it fails one night, it can be detrimental to the chickens as they will be reliant on it to keep warm that if the outside temperature is much colder than the coop was thanks to...
She is almost constantly looking up? It does seem like wry neck is a good possibility. Give her the vitamins Wryop Rock recommended. You will need to stick with it for a few weeks and give it to her daily. You will not see progress instantly but keep giving it to her.