Julie is the key to save everyone (not the kids)

So Julie as a story walker can do nothing but watch past events and risk herself getting killed (or maybe just her mind). So what she can really do? Understand who the man in yellow is, his behavior and powers and identify who he is on the current time. That would give a chance to people survive the massacre. But honestly he is so overpowered I'm yet to understand why he simply doesn't go and kill everyone on his own right now.