Move on. The specific issue you describe it irrelevant- she's looking for a reason to break up with you, and that is what she found.
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On the other hand, it could be that she feels the need to go out and try new things. She's been with you for six years, through most of highschool. I'd wager she's starting to wonder what other people are like. So she might be trying to break up with you not because she has any particular problem with you (other than that you're familiar) but because she doesn't want to cheat on you.
So, provided you don't make the split too acrimonious, it's possible she'll go out, realize how shitty dating new people can be, and come back. Depends if you want to be in that position. If you can handle her fucking other people, forgive her, and take her back when it doesn't work out (and have this cycle repeat periodically), it's up to you.
She's just wondering if she's with you because she's been with you for as long as she can remember, or if she's with you because you're really the one she wants. If she decides that you are the one she wants, and you're still around and available, you two might be better off in the long run.
That said, I'd still recommend moving on.