Call her maybe an hour or 2 before the date to see if she picks up. If she doesn't or her phone is closed, she's flaking. Move on. If she does answer, it could go 2 ways:
-The last minute flake : She responds but gives you excuses as to why she isn't going to come
-Not flaking : She simply answers your phone call and asks u what's up. If that's the case cool that means she's still on for the date u don't need to ask her anymore. Just tell her you might be a bit late by 15mins and say see u later.
If she flakes last minute, you don't want to be reactive but you do want to stand up for yourself. Maybe her interest is low and she wants to take her time to see how u react. In that case u say "It's not cool that I had to call you to know that last minute, I freed up time on my schedule for you.", pause and let her say sorry.... then say "ok, when you really know you can keep your word for a date with me contact me. See u" but in a calm tone of voice.... if she has anykind of interest she'll reach back within a week or two, but don't wait for her to do so just go date other women in the meantime.