Look, here's the rub..there are 3 possibilities here, none of them great:
1) She's serious about the whole "moving too fast, I don't want a relationship" thing, in which case, if YOU do (and by your post I'm assuming that's the case) you leave her alone and move on
2) She's playing head games with you, for WHATEVER reason, in which case, if you're looking for a relationship, this is NOT the girl you want to be with, and you should move on. Trust me. Move on now and avoid the drama and BS later
3) She met someone else, has an ex-boyfriend issue...whatever....in which case you want to move on, for obvious reasons.
If you REALLY want to pursue it...don't. Lose her number and wait on her. If she comes back from "the great flakeout", during the first phone call, text conversation, face to face...make it quite clear you're not going to play head games. No "who's chasing who", no "where do we stand", no "I want you, I don't want you". That's all bullshit. Let her know that you don't need to jump straight into a relationship..that's fine...but you do need to be honest and open with each other.
All of these are good hypotheses. But perhaps the best thing to do would be to stop worrying about what she is thinking and get on with your life.
Not meaning to sound harsh and unsympathetic (I know first hand how much it sucks when 'great' girl flakes out), but there are zillions of possible reasons why she could be acting this way, most of which have nothing to do with 'Gunnerone84'.
Could she explain 'why' she did this. Probably not. It's generally accepted that women are more in tune with the emotional part of their brain, and therefore her logic may tend to be more 'fluid' than that of a typical man. And, let's be honest, can any of us (men or women) explain why we do half of the stuff we do?
So, my advice to 'Gunnerone84', and to all of you having realtionship trouble, is to stop worrying about what the your other half is thinking, don't take it too personally and, as 'Pilferk' suggested, talk to them openly and honestly about your issues.
Good night, god speed and good luck.