Wild Magic by Tamora Pierce
Daine is desperate to forget the past. The bandit attack. The slaughter of her family. Her madness. Calling to the wolves, running with the pack, smelling blood, smelling vengeance. But she cannot forget. Power over wild magic is Daine's birthright, and protecting Tortall her destiny. For her adoptive home is in terrible danger, being ravaged by dread creations from the Divine Realms: Stormwings, Hurrocks and deadly Spidrens. Daine must master her rare and wondrous power or else see friends and home destroyed once more.