Daughter of Sun, Bride of Ice - Ice & Fate Duology, #1

To save a kingdom, she must lose her heart. Born a princess in a land where the sun never sets, Arynne longs for the freedom to use her inborn magic. When an emissary from the dark side of the world requests an alliance sealed by marriage, Arynne jumps at a chance to escape the rules of her homeland, even if it means marrying a prince she's never met and never seeing the sun again. The starlit kingdom of Frorheim believes that only a marriage of a Solean Sun Princess to their Star Prince will thwart the return of a feared sorcerer.
Arynne meets the qualifications, but the journey is perilous. Even more dangerous to Arynne, however, is her growing attraction to the roguish Frorian soldier, Kajik. In the throes of true love, Arynne rues her betrothal to the unknown prince. Can she follow her heart knowing that if she forsakes her vow, Frorheim is doomed, and herself along with it?