She's telling him not to do "it." What is it?
Sounds like something pre-planned. Otherwise, if she knew nothing about it, why wouldn't she say something like "I'm here" or "I'll help you" or "Do what they say" or "Just lay down." Or a million other things besides "Don't Do It!"
It would seem like they had discussed something beforehand. At the very least, she knew at that point he had a gun in his hands.
If he actually had a book in his hands as she said, and she knew that to be true at the time, who would ever say to someone "Don't Do It!"
