Hallowed (Unearthly Series #2) by Cynthia Hand

For months part-angel Clara Gardner trained to face the fire from her visions, but she wasn't prepared for the choice she had to make that day. Now, torn between her love for Tucker and her complicated feelings about the roles she and Christian seem destined to play in a world that is both dangerous and beautiful, Clara struggles with a shocking revelation: Someone she loves will die in a matter of months. With her future uncertain, the only thing Clara knows for sure is that the fire was just the beginning.