Raelia : the Medoran chronicles. Book two / Lynette Noni.

Upon returning to Akarnae Academy for another year, Alexandra Jennings quickly discovers that with Aven Dalmarta still at large, life in Medora is anything but easy. Knowing that the banished prince hasn't given up on his goal to reclaim his birthright, Alex seeks out the Lost City of Meya, searching for what remains of the immortal race. But never could she have imagined finding what she does. Caught up in a tide of events beyond her control, Alex learns that when Aven tried to Claim her at the end of last year, something in her changed. She's not sure who-or what-she is anymore. All she knows is that if she fails to stop him from finding a way through to Meya, all hope for the people of Medora will be lost. And it will be all... her... fault.