Step 1: make your "hangouts" things you would do whether she came or not. This way it doesn't matter if she flakes because you are doing something you enjoy rather than making a special time in your schedule for her.
Step 2: Somewhere in your initial interaction, throw this in:
YOU: I have really high standards for the people I allow into my life.
HER: Oh really? Like what?
YOU: Well for example, if a girl ever flaked on me, I probably wouldn't ever take her seriously.
Cuts flakes in half right out of the gate
Hope this helps.
Your boy,
870