Ruby fell back, trapped by the monster. However, just because the creature had her leg in a vise grip with its teeth, didn't mean Ruby would be paralyzed with the pain. Wrapping her other leg around its head, and getting it in a headlock, Ruby slashed violently at the beast's throat, from the jugular to the brain stem. 

(Edit:This, of course, is the course of events if the vampire doesn't let go.)