Yea, I was sort of expecting it, that's why I spent quite of a time above and recommended lots of patience in stead of just ]"next". Next is still probably the best option, but it may not be the most optimal one, if that makes sense...
Once you create a good connection with the girl (and you did), she will always remember you as a great guy. Does she want to dump a great guy? If she is normal she would not, and if so she would have to feel quite guilty about it. Which is BTW the reason why girls try to blame the guys before the break up, they make it seem that it was all his fault and they have to justify it to themselves, so they don't have to feel guilty about it...
She doesn't want to dump you but at the same time she may not be open or ready for relationship. So what she does is, she wants to keep you around as a sort of an Orbital. But remember, you've already slept with her, so this is a different sort of Orbital that is usually described here on GC, she's already created a good intimate connection with you, so you are simply orbiting but in much closer Orbit then guys who are interested in a girl but never slept with her...
So simplest way to deal with it is to remove yourself from the Orbital, simply Next her, forget her...
But there is another way, more advanced, which is to remain in the Orbital.... This requires lots of patience as described above... You just don't know when she may reach out to you - it could be couple of days, it could be weeks, months... But it could also be YEARS. And it could never happen as well, you just don't know. It is a game mostly with your feelings, because if you keep thinking about her and try to somehow "get her", you are constantly investing into her while she keeps distance... You may suffer a lot because of that...
So a good way is to keep the possibility open without investing into her. Simply remain open to her while at the same time you are focusing on another girls (as you do). Anytime she contacts you, you show an interest. Anytime she pulls away and go distant, you don't chase, you let her go, you go distant yourself...
What I would do in this situation is, I would create sort of a game in which she is investing into you (you are already doing it, she is investing into you by keeping in contact). She may be wondering why you are not chasing because she knows you are interested, but all you have to do is keep showing an interest in her and in her life. In this situation I would remain passive (since she canceled the date), I wouldn't ask for another date - it is her turn to show that she wants to see you. So once she does (and hopefully she will) it is a good sign. At that time I would stand up to more leading position, suggest the date and place where to meet. She will most likely accept since she is the one who offered, yet at the same time you are remaining in charge by selecting where and when... Then go from there...
Keep us updated, it is an interesting story.