Trickster's Choice by Tamora Pierce
Alianne has an oppressive heritage. She is the daughter of Alanna, Lady Knight and King's Champion - the foremost warrior of Tortall. Aly is not a fighter - she hates her mother's obsession, which constantly takes her away from her family and makes her children feel neglected and resentful. After a stormy argument with her mother, Aly runs away to make them sorry. But she gets more than she bargained for when she is kidnapped by pirates, and sold as a slave in the far-off Copper Isles. Aly's future is bleak, but then she finds out that this has all been planned, by a god, no less. Aly is a favourite of the god Kyprioth - she is the Trickster's Choice.