It doesn't matter what most people do. The onus is on cops to not shoot unless it's absolutely necessary, not on the rest of us to navigate around their trigger-happy nature. It may be smart to do that but it doesn't change where responsibility actually lies IMO.
You said the agent overreacted, so to me it's that simple. The guy with the gun overreacted and someone is dead because of it. I don't see the need for the "she shouldn't be there" thing, because she wasn't doing anything that is supposed to be punishable by death to me