Ok! this isn't going well. My advice:

Text her saterday in the evening, you'll be 15 min later. Cause you'll have to stop by a friend to drop a book. So replace the appointment 15 or 30 min later.

So she has been reminded about the meet up. Now she can 1) cancel/no reply or 2) answer positive.

Case 1) She cancels: Say that's no problem, you guys will meet up soon. Remove her number and forget her, don't answer further texts, unless she calls you. If she calls you, explain you had it quite busy and was planning to call her in 2 days. Then call her the next day, say it's quite irritating that she is cancelling always and you surely want to meet up. Arrange a meet the same evening or next day. She doesn't call => remove number, forget her.

Case 2) positive answer: Meet up

As I always use when things aren't explaining themself: find a little thing to check how it's going (like the 15 min later). If the 'test' is negative, give up. If the test is positve go on. But don't waste your time on such stupid sh*t. Don't keep trying on and on, maybe they enjoy, you'll feel like a lozer. The have to be the lozer in there games! If she doesn't answer, leave her. Probably she'll be questioning why you aren't trying more, she loses

At case 1.1) she calls you, I'm starting to play the same game. If she's get the point, she won't reply. If she really want to meet you, she'll excuse and show up the next day.

If you feel she's joking around => DELETE HER

JustAsk's ideas seems pretty solid. Ive had a girl play this game with me a little bit too. Ive asked her out a few times and she always cancels hours before. Then she asked me to go to a costume party and I shut her down, so the next week she canceled on a football game with me. I just texted her "youre such a flake. Youre lucky you're pretty, but even looks become obsolete at some point" and havent tried to conteact her since. It does kinda sound like a little oneitis to be honest. This chick im talking about is probably the hottest one im talking to right now, but ya know what? At some point, the sh*t has to stop. Drop her man. Let her be. If she contacts you, just roll with it, then cancel on her at the last minute and see if she comes around again. If she tries to set something up for a second time, then you can resume your pursuit. At this point though, forget about it and deal with the other girls you should have ready...