I grew up in the Arctic, in a wood-heated house. When it's cold, one quilt won't be enough no matter what batting you use. Here are three options I would recommend:
1. Use Warm and Natural, with a flannel backing. The flannel makes it warmer, and keeps the quilt from sliding around if she layers multiple blankets/quilts.
2. Wool would be even warmer, or a layer of wool with a layer of W&N.
3. Warmest of all would be to make the quilt, then attach an extra back to turn it into a duvet cover. As long as she isn't allergic to feathers, a heavy feather or down duvet is the only single-blanket way to stay warm in a really cold bedroom. If you quilt the top like usual, it can also be used just as a quilt in warmer weather.
Whatever you choose, I'm sure your friend will appreciate it!