ok, I haven't seen any good advice for you yet in this thread, so I'll try to input something useful if I can. I went through the same experience recently, 2 dates with a nice girl, then she suddenly dropped off the face of the earth for no apparent reason.
What I'm getting at, is this is so typical in the dating world. It often takes several tries until you finally find someone worthy enough to be in your company. I'm not sure how old you are (I'm 23 myself, so I know that a lot of girls in their younger 20's can be quite flakey). I mean, she may have been interested you while you were out with her, then had a sudden change of heart for petty reasons. Women analyze things WAY too much and can be highly influenced by their friends. This reminds me, did you ever watch Seinfeld? Remember how petty that group was in dumping people? Sometimes I wonder if people really are like that....
In short, don't try to contact her again. The ball is in her court if she wants anything to do with you. Move on to somebody better.