I read-up about sunlight for this post. Was surprised to find that 5-10 minutes of sun exposure for just 2-3 times per week can elevate Vitamin D levels. Perhaps your daughter’s problem is absorption-related.. Due to other medications which can interfere.
If your far north staying in the sun won’t help unless it’s mid-summer. My doc said I could stand out all day in my skivveys in the winter sun and get 0 vitamin D.