Hmmm rather than Saki killing Miyoko, I feel that the title is hinting at the opposite. You know the irony where the one who keeps shouting "I'm killing you" ends up dead? Yeah, exactly what I was thinking whilst reading this
Would make sense, as she'll probably want to turn her so both are vampires.
The way I see it at some point other vampire hunters will turn up for dramatics(tm), then Miyoko gets corned (possibly protecting Saki), so Saki sacrifices herself in turn. Miyoko gets pissed and kills the hunters (or chases them away or flees), then turns Saki to save her.
The End.