Without getting into a bun fight Artie, I have to disagree. If you use a 'L' mount plate for portrait mode you don't have a problem, but if you have your gear mounted normally on a ball head, and you flip it to portrait orientation, you are asking an awful lot from a single 4mm or 5mm fixing point. Even a DX camera plus kit lens is nudging 1kg.@ Arthur......The comment about anti twist plates is actually incorrect. A properly designed plate doesn't need these anti twist plate designs, and I've personally ground flat two of my (expensive!) plates so designed, so that they now fit on any camera I own. They don't twist on any of the cameras I own, even the lil cheapy P&S my daughter owns.
And of course your daughters little P&S won't twist. It only weighs a tad more than a feather.