I agree it's a very random fall off. She may have backwards rationalized that the date wasn't as good as you thought it was, or maybe there is something personal going on behind the scenes.
Since you've already asked her about her schedule twice and triple texted, I'd give it another week and then send "I genuinely didn't take you for the flakey type." If she doesn't respond to that, take the hint and move on to the next.
