fantasy book series: woman seems like new type of vampire, recruited by paranormal police after feeding on some vampires

[Lori Blank]

SPOILERS INCLUDED: The first book in the series was about a woman who's guardian dies (I think in a car accident) and when she goes out into the world for the first time she starts to get really thirsty/thirst pains. She ends up in a vampire club and ends up feeding on the vampires not the humans. She is recruited by a paranormal police division and the doctors there name her an emperor vampire or something along those lines. At one point you find out she's not really a vampire but a demon.