An odd thought: it will be a dramatic irony if the innocent is killed by Bellatrix. That would actually tie together the two Sybill premonitions/awakenings (first part of a prophecy is set up by Bella getting out; second part by Harry's resolution to kill the villains as fast as possible on the death of an innocent; another part still to come will be triggered by the death of the innocent itself at Bella's hand. Sybill doesn't understand the whole picture yet, which is why she can't articulate the whole prophecy.)