Let go of those dreams.
You know why? Because there is work. And most teachers don't teach, so instead of soul-searching, you'll be searching for a tutor. Because you might come back from vacation, hang out with your friends and have a great time, but when you two get to school then you may find that you will be ditched for a group of people she's met through cross country.
Now, NEVER get mad that your friend has other friends. However, you have the right to get pissed off if ever time you try to talk to her she SPRINTS down the stairs ahead of you, not even acknowledging that you spoke.
Why this happens? Hard to say. Her new friends are nice, so it's not their fault.
It's something wrong with your friend. She's probably 'moved on' or she thinks that she is somehow above you now. Either way, after six weeks of trying to get her to talk to you, I'd say it's about time to take the hint, give up, and sit somewhere else at lunch, because this piece of unexplained phenomena will only drive you mad, and she might even start to miss you once you've given up the chase. Show her that you really don't need her at all, and maybe her head will deflate.
Basically, she'll stop running once there's no one chasing her. Then wait a month, and if she hasn't started talking to you, then maybe try to start conversation with her, if you still want to be friends, that is.
But note the 'maybes' in this post.
P.S. Writing really does help! At the beginning I wasn't sure what to do, but as I wrote I found a solution! Man, this is awesome!