Well, of course, it was bad of the little girl to lie, but little kids lie. Making a spectacle out of disgracing a 6-year-old is disgraceful. After failing to check the very checkable fact that made the company think of her essay as the best, it should have quietly resolved the matter with the girl's family — probably by sending her on the trip anyway — and given the prize — the honor of winning plus the trip — to someone else.
I'm not sure about letting her go on the trip anyway, but I do agree that it's a bit out of bounds to pile on this girl. She's six. Not sixteen, not twenty-six, but six. As suggested in the comments, I think her mom had a hand in this, and at the very least should take the blame for not vetting her daughter's work (Don't you need parent's permission for these things, anyway?), not to mention the judges, for not vetting properly.
This ought to have been discreetly, and this girl shouldn't be subjected to this, as this goes well beyond the realm of a moral lesson.
I have to wonder though, are young girls that hung up on Hannah Montana, as to even allow such a situation like this to arise?