The Spell Keeper — M.J. McGriff

Zuri Abayomi doesn't need her nation's eccentric oracle to reveal her destiny. She's going to become the general of her father's armies whether she likes it or not. But not even she can go against tradition. On Zuri's coming-of-age day, the oracle sends her on a strange quest, far away from her people and into the territory of their sworn enemies.  Find the serpent slayer and the one who would never be king. Give them what's inside the Oracle's mysterious little box. Discover her destiny. But her path looks nothing like she imagined.  When dark magic brings to life an evil sorceress and her shadow griffins to terrorize the Griffin Vales and bring about a civil war that's been brewing for centuries, Zuri must set aside everything she thought she knew and take up the ancient magic of the Spell Keeper.  And, for once, she can't do it on her own. It'll take the help of another magic wielder, a nun-turned treasure hunter, an ex-order captain, their motley crew of pirate friends, and—by far the worst—the prince of the nation she's been trained to destroy. Yet their efforts won't be enough to defeat an evil sorceress and stop the destruction of both nations if Zuri can't find a way to heal a past she's fought hard to forget in order to unlock the magic that's always been inside her.