Cops aren't required to issue a warning. They are allowed to use deadly force when they know innocent bystanders won't be harmed and when they believe delay will cause serious injury or death to other people. For example: when the wanted criminal who routinely kidnaps and tortures people is beating your face in while sitting in top of you and refuses to freeze or put his hands over his head.
Honestly, I think I may be arguing her side too much out of obstinancy. I think it's clear that she let her overall mental state influence her decision. Still, her side is technically legal. His is not; not the break in, not the assault/torture of a suspect, not the assault on a police officer, not taking her gun. None of it.