I can't see how it is "primarily" an American event. Sure the US played a key part and took considerable losses, and President Obama is certainly welcome to come and represent them. But the British and Canadian forces (remember The Queen is head of state of both countries) deployed more men on D-Day, and over the whole campaign took many more casualties than the USA.
If the British government, who should have organised everything, has messed this up, then it does seem time for The Queen to take Brown to one side and say : "Look, you've hacked all the rest of the country off with your various stupidities, now you've hacked me off. Push off".