"So I've come up with my own law: Let people carry whatever weapon they want, as long as it is openly displayed."
That's already the case in the great state of Arizona; any WEAPON that is legally owned (including rifles, handguns, shotguns, and Class III and NFA weapons) are legal to carry openly without a permit and concealed with a permit. I guess nobody told her that, however.
As for Washington, D.C., I wouldn't worry too much about it. The only people who'll be carrying handguns outside the home are the criminals and gangbangers. Wait, they're already the only ones carrying handguns outside the home!