Queen of the Conquered (Islands of Blood and Storm, book 1)
From the publisher:
On the islands of Hans Lollik, Sigourney Rose was the only survivor when her family was massacred by the colonizers. When the childless king of the islands declares he will choose his successor from amongst eligible noble families, Sigourney is ready to exact her revenge.
But someone is killing off the ruling families to clear a path to the throne. And as the bodies pile up and all eyes regard her with suspicion, Sigourney must find allies among her prey and the murderer among her peers… lest she become the next victim.