Scarlet Curse by T.H. Hunter

After the total disaster at the prom, 18-year-old Rebecca “Beccs” Flynn is devastated. Haunted by humiliating memories, she spends the rest of the summer caring for her grandfather. Little does she know that her woes are far from over.
Thrown into a world she never knew existed, a world in which the uneasy truce between vampires and slayers might break at the slightest provocation, Beccs finds herself number one on the slayers’ hit list . She has the Scarlet Curse, an extremely rare form of Vampirism that provides her with extraordinary powers – a threat the slayers are determined to stamp out.

Rescued by Raphael, the arrogant yet handsome heir to the Vampiric Throne, her only chance of survival is to seek refuge at the Royal Stronghold in Romania, which also serves as the most prestigious college for Vampires worldwide.
But the vampires are divided. The familiar college flair of the castle quickly spirals into an atmosphere of vicious intrigue, lies and suspicion. To avert a civil war, Beccs must work with Raphael, of all people, in order to survive. Quickly, they discover they have a lot more in common than just survival.

The enemy, however, is already within the walls.