Anais had a very high level of bloodlust for a Dhampir.
Ever since she was accidentally turned, she had been experiencing vivid hallucinations of draining her fellow students. However, when ever she was around the blonde haired teenager that had turned her, the bloodlust was extremely lowered.
The book Xavian had recommended, 'Dhampir: Facts and how to kill them', had said that it was due to something called a blood bond, but she did not really bother much about the details.
All she knew was that Xavian had made her this way, and he would take responsibility for it.
That was her own way of taking revenge on the blonde haired teenager.
Thus, she had accosted him and made him promise to accompany her to the ball.