I live in Minnesota, and you know how cold it gets here.
The horses that i take to the World Show are always slowly acclimated again when they get home. I start off by blanketing them in and out of the barn.. After a while I let them out during the day without a blanket, then but inside at night with a blanket. Later they are turned outside 24 hours a day, but still wear blankets at night. Eventually, they no longer wear blankets at all.
They are in an area with really good shelter. Eventually, I do not blanket them at all and when I notice that they are not shivering at all, day or night, then I put them out in the paddock areas they will stay in for the winter. At this time, all but one are now out day and night without blankets (though it is going to get really cold next week and I may have to blanket again).
The one, she is taking really long to grow any coat, so she is out during the day (weather permitting), and in the barn at night, with a blanket at all times. The blanket she is wearing includes the neck. She may have to be in and out of the barn all winter.
I do know that the southern horses are very slow to acclimate to colder weather.
Good luck with her.