Looking forward to seeing the conversation,to be honest, it will probably help out a lot more than your description haha. Regardless, from what I can make out there is a chance that she actually has just been busy/has an excuse to not message back etc. There is also a chance that because you had a change of plans that she possibly felt as if she was less important and had a change of heart (even though she mentioned the alcohol and shit), or that she felt you were coming on too strong.
My advice would be to play it cool. You don't NEED to hang out with this girl, which is why you should act in a similar fashion. If you don't get to hang out over the weekend or whatever, then just try to roll with it. If she does text back after there your planned time to hang out, again, act cool and make sure she knows that you don't care and that there will be another time.
With this being said, I genuinely hope this is not a situation where you are are being used to get her alcohol because for some reason she cannot buy it herself. That would blow. Which is another reason you should build up rapport, and more specifically sexual tension. If she is really into everything you are talking about, then you shouldn't have a problem F-Closing/dating/whatever you had in mind.
If she does completely flake, search the fourm for what to do in that situation. Something that comes to mind would be
list-of-text-messages-game-vt21175.html Which could be applied to your texting/facebook messaging game and includes a couple "openers" to be used with flakes.
Good luck.