Darkstar Rising by Susan K. Hamilton
Live by the sword. Die by the sword.
Youngest daughter of the ruling house of Illauren, Princess Kiara - the Darkstar - has worked tirelessly to undermine the rule of the Pretender-Queen, Ushan, and restore her brother to his rightful place on the throne.
Now the time has come, and Darkstar is riding out to bring the people of Illauren to her brother's side. But an accident changes her plans.
Darkstar suddenly discovers secrets about herself that have been hidden since childhood. Secrets that will transform her from an ordinary princess into one of the most powerful women on the continent. And with that power comes choices. Choices that may change the course of history itself.
Choices that could destroy everyone and everything Darkstar is fighting to protect . . .