OK, let's think about this.
What are the options?She likes you as a friend and is wary of answering texts too quickly in case you think that she is more serious about you than she really is.
She cannot get on to a computer, because it isn't working / she isn't allowed / there's no privacy for dealing with personal mail/ etc, but she would like to get back to you quickly, if only she could.
For some reason, your e-mails & texts didn't get to her. Maybe she isn't allowed to use her PC or phone, perhaps.
She read and enjoyed your messages but didn't realise that they require replies.
She's a bit shy and doesn't want to appear too keen to be involved with you.
She isn't as committed to the relationship as she was, and as you appear to be, possibly because of the distance between you and other things occupying her time.
There may be more reasons.
However, she either likes you, and wants to try to make the relationship work, or she likes you, but doesn't want to pursue the relationship.
If it's the former, then all's well.
If it's the latter, you can try to convince her.
If, however, her feelings for you have faded, then, yes, you will be sad for a while, but it would be for the best.
You wouldn't want a relationship based on pretend feelings.
I know that teenage love can hurt ~ we have all been there ~ but you may not even have met the girl who will turn out to be your soul-mate, so don't be disheartened.
What to do now without appearing too needy or clingy?
You could give her a ring and check the details of the concert ~
confirm the time, check ticket details, etc.
Will you meet her there before the event?
Is she actually in the concert?
If so, you could ask if she is nervous and wish her luck.
Rehearsals may have been taking up her time, which might explain why she hasn't got back to you.
When you actually see her, you may be able to judge her feelings a little better, but, perhaps, when she is less busy with the concert, you could just ask how she feels about having a 'Semi-long distance relationship' and if she is happy with it?