Sea Glass by Maria V. Snyder

Not bad for a student.

Glass magician Opal Cowan's newfound ability to steal a magician's powers has made her too powerful in the eyes of the council Despite being under house arrest, Opal travels to the Moon Clan's lands in search of Ulrick, the man she thinks she loves. Thinks because she is sure another man, now her prisoner, has switched souls with Ulrick.

In hostile territory, without proof or allies, Opal isn't sure whom to trust. She can't forget Kade, the handsome Stormdancer who doesn't want to let her get close. And now everyone is after Opal's special powers for their own deadly gain