It's estimated to be over 300, at least. There's pretty interesting stories on how she did it too. Makes you wonder.
The worst serial killers are supposed to be males, but I say she was waay more disturbed then any male serial killer known. I mean she used to stick needles into a girl one by one till she bled to death. =O
So she scares me too, but hell. Vampirism relvoves around sex and violence so it's no shock.