Why do you even have to kill her anyway, I mean all you need (its all you get anyway) is a little vial...yeesh, just ask her for a blood sample or something, or at the very least...(walk by her) hum hum...(prick! take sample) "oops, sorry, didn't mean to prick you with my sword...I mean she is HUGE, I'm sure she could spare a LITTLE blood.
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"Not everything ends the way you think it should"