I hate how this article focuses solely on her stupidly and completely glosses over the glaring failure of TSA to prevent this from happening in the first place. Bottle of water is treated like a WMD, but a pistol? Nah, good to go. 'Murica...
Also, I low-key think she deserves some punishment for having such a tacky gold plated 1911 in the first place...
They had me excluded interviewed, to the point of missing a flight, because they found a phillips screwdriver bit (no screw driver) in my back back. Even reminding them that airlines exclusively do not use these screws in anything inside the cabin of importance, had no effect. I totally agree with your "comically incompetent" phrasing.
You're allowed to fly with a gun (in a checked bag), and it doesn't make sense for TSA to enforce a law in America that isn't a law in America. It makes more sense to let them get to Australia, where they've then broken the law, and arrest them there when they get off the plane.
You can fly with a gun in the US as long as it is in a checked bag. As long as it was in her checked bag and stored properly then the TSA has no reason to care. It was on her to know what is and isn't allowed at her destination.