Now I know why Kou-kun calls her masochistic kitten.
Masochist: a person who derives sexual gratification from their own pain or humailation
I think all of the vampires can feel that she enjoys it. That's another reason why shu calls her a "slut" and now I know why she stayed there when she had a chance to leave. I honestly thinks she likes the attention. She probably fetish them and when she get bit she tries to act like she doesn't like it but you know she do because she doesn't resist it.