Hidden Angel by Tamar Sloan

Angels and demons have battled for millennia. Their inevitable war has begun.
When Gabby arrives at Mercy Academy, she’s never been more excited. This is her chance at normality. But within minutes, she runs into cranky-pants Colt. Their resulting argument gets her on the Dean’s radar, but she can’t explain her unease about the mysterious guy.
Then, unusual things start to happen. Memory lapses. Mysterious murders. Beings with red eyes skulking in the shadows. And it turns out Colt is one of them. A demon.
When she’s attacked, Gabby’s forced to face the truth. She’s an angel. One who’s far more powerful than she could have imagined. And the academy is the battleground for the festering hostility between angels and demons, one that blurs the line between good and evil.
Gabby’s going to have to decide. Whose side is she on? How can she save others as they become collateral damage in this supernatural war? And if she’s an angel, how can she have feelings for Colt, her sworn enemy?