Why would she necessarily have to prove that? It would certainly help; but in any jurisdiction where use of deadly force is permitted to defend yourself from imminent and not otherwise escapable harm, pointing a gun at people who break down your door by surprise at some ghastly hour is an entirely legal (indeed, frequently valorized) activity.
Conducting a no-knock raid (and on such dreadfully flimsy "evidence" no less, is deliberately and knowingly creating a volatile and potentially lethal situation in a way that just knocking on the guy's door, or calling him and telling him to come outside, or hailing him with a loudspeaker, or about a zillion other not-terribly-difficult approaches aren't.
Cop-immunity is a hell of a drug, so it wouldn't surprise me if they get off with a slap on the wrist; but that doesn't change the fact that the cops knowingly and deliberately created a situation indistinguishable from armed home invasion(because, for the most part, it was...). The resident doesn't have any special duty to not self-defend because the gunmen he can probably barely see might be cops rather than robbers, and it's the cops who knew full well, before they went in, that their behavior was virtually certain to trigger a self-defense response in anyone who has one (that's why they always bring the flashbangs, body armor, and overwhelming force to the no-knock raids).
As noted, it would certainly help their jury-appeal if evidence turns up that they just pumped a harmless old guy full of bullets; but the police conduct in that situation would still be deplorable even if (by some probabilistic quirk) the victim had managed to terminate the entire raid team without taking a scratch.