A Turn of Light — Julie E. Czerneda

The village of Marrowdell is an isolated pioneer community, but it is also the place where two worlds overlap, and at the turn of light- sunset- the world of magic known as Verge can briefly be seen.

Jenn Nalynn belongs to both Verge and Marrowdell, but even she doesn't know how special she is or that her "invisible" friend Wisp is actually a dragon sent to guard her and keep her from leaving the valley. But Jenn longs to see the world, and thinking that a husband will help her reach this goal, she decides to create one using spells. Of course, everything goes awry, and suddenly her invisible friend has been transformed into a man. He is not the only newcomer to Marrowdell- and far from the most dangerous of those who are suddenly finding their way to the valley...