I know that I was searching out the meaning of the "I rebuke you in the name of Jesus" as well as the significance of boiling water. Both have spiritual significance with boiling water being a force of protection, spiritually. And the rebuke statement is also a statement of protection and banishing of demons.
So when she asks "Why you moving away" and he responds "Moving away from your hot steaming water." She repeats what he said, laughs, and then says "I rebuke you...." I really believe that at that moment, she was being playful, making the connection between the boiling water and banishing demons. (Or maybe she was literally boiling water to protect herself from the suspected prowler, and her auto-response to his reaction to the water was to make the statement she'd been making in her head about the prowler?) When he went zero to 60 at that comment, she was shocked, I think. The situation turned unnecessarily from a joke to life or death so fast. IMO.
I am curious about the shooter's background, because if he was abused in the name of religion, or had been deeply shamed via religion (i.e. religion used in monstrous ways) then I could see it being a hair trigger. Of course not an excuse in any way shape or form. He was clearly not fit for duty or service of any kind. Sonya did NOTHING to deserve or warrant her murder.