Was the Deadgirl one of the Re-Animator Experiments?
That's the only thing I could think of as her origin is not explained. She is similar to one of Dr West's experiments from RE-ANIMATOR and its sequels.
sharea necro response seems appropriate in view of the subject matter.
the Re-animator stories had an injected serum to cause the revivification of dead bodies, but I don't believe there was any contagion via bite.