Sometimes I have doubts about this whole "put the ball in her court" thing. I mean in theory it should make sense, don't spend time chasing someone that keeps bailing and giving half-assed excuses. Sure, I buy that completely. However, my experience with many women has been that they are utterly terrible at taking the initiative, even for things that they really do want. Be it going in for the first kiss, initiating sex when you're not a couple yet (i.e. when it's not a given if you get what I mean), or asking the other person out. Back when I was way more awkward with women than I am now, I got rejected more than once because I "wasn't assertive enough". I've had girls over at my place and not made any kind of move at all (even though I wanted to), and afterwards they say I seemed awkward because I didn't make a move.
My point with all this is obviously not that you should beg for a girl to go out with you after she's being flaky. My point is however that "putting the ball in her court" doesn't always pan out, even if the intent is good. She might not be as assertive as you hope she is. Instead of just giving out your number and dropping her completely, you might reach out in a week or two and ask again.