some unsolicited advice: next time a chick cancels on you, just say "it's cool..." nothing more. don't offer to re-schedule, wait for her to offer that option. that way you know for sure what her intentions are. if she doesn't make an attempt on her own to re-schedule, then you know she doesn't care that much and it's bushes. if she does offer, then it's a clue that maybe something did come up and then you can either accept, refuse etc, if you can't make it the day she says then the ball is back on your side and you make a counter-offer, and so on...
EDIT: also if she offers to re-schedule, if she also makes a gesture to make it up to you (for example offers to buy you lunch to make it up to you, offers to buy you a drink, offers to take you for a visit of whatever even if it's free, etc) it's also a good sign that she was sincere. it's not the fact that she's offering to pay for something, doesn't even have to be a big gesture, it's the fact that she's making a gesture to make up for the inconvenience she caused you. this shows she values and respects your time.