I had this awful nightmare lastnight (warning...graphic)?

Sometimes our dreams reflect buried emotions and they are played out carefully for you to experience. You mention the little girl trying to end her father's misery; a normal person, let alone a child, wouldn't have the mental stability to pull it off. Maybe the child did what you would've done? I don't know, but you may have something in your past that may help you figure out why you dreamt that.