It's a tough one, because from a kid's perspective it can be a really big, really remembered (for ever) type of exclusion. I clearly remember being nine and not being invited to a girl's birthday party, even though I'd expected to be and had even gone out and bought her a present from my own pocket money.
And it's funny, because I don't remember that much from my childhood, but this seemed to stick.
For what it's worth, she seems rude at best. You're better than her, so rise, rise, rise above it.