Sister of Starlit Seas by Terry Brooks

A rebellious young heroine sets off on an adventure of self-discovery in the third novel of an epic fantasy series set in the world of Viridian Deep, from the legendary author behind the Shannara saga.

Auris’s adoptive sister Char has always been the baby of the family—a position that grates on her, especially when everyone is so intent on telling her exactly what to do and how to do it. Plus, there is her headstrong, impulsive behavior, which her family has always seen as a liability. But Char is certain that the quality most see as her greatest weakness is actually her greatest strength: her willingness to instantly brave danger and leap to the rescue the minute anyone she loves is threatened.

Char knows she can never grow into the woman she was meant to be under her family's loving but repressive eye, so a month before she turns fifteen, she runs away, and ends up joining a Human pirate crew in the warm, southerly regions of her world. But three years into her pirate career, her captain—and the man she is convinced she loves—is captured by the those in charge of the slave trade he has been fighting. And when Char leaps in to rescue him, she suddenly finds herself thrust into an adventure that will uncover secrets she never suspected about herself. And which will maybe, finally, teach her to look before she leaps.