Hold her too it...also make sure when your planning on meeting for the first time, its incredibly nuetral and no pressure.
When you set the meeting up aim for it to be as friendly and inviting as possible (interesting) while at the same time requiring little commitment. In other words, set it up like a meeting with a friend, not a date. Do something and meet somewhere that they will feel safe and doing something that they can leave if they get uncomfortable.
For instance, agreeing to meet over a cup of cofee or tea. Even add in something like "Lets do starbucks, i don't have a whole lot of time that day i have to be somewhere, but this way we can chat and get to know each other."
Its almost like a mix of FTC and disqualifying. Its alot like when you goto a set and tell them you cant stay long bc you have x,y,z to do. Do the same thing when you plan to meet someone for the first time. They may be more interested and willing to meet if the window of time seems short in thier minds.
Also, if you have established any kind of banter with her, then bust her balls for it. "Well, ill forgive you this time...but your not getting off easy now you owe me a drink
" or maybe "Ok i see how it is, don't let this become a habbit because having your uncle die 10 times or saying your dog ate your homework wont fly...ill catch on eventually!"
You wana handle challenging them on the topic the same as escalating anything else, start subtle and then pump it up the worse they get. If it happens a second time simply tell them, "Look, if you don't wana get together let me know so i can play my time else where, im not made of glass i can take it." or "You know my time is important, when i make plans i stick to them. Hopefully your not one of those people who cant hold plans."
And lastly, if they keep doing this, stop putting yourself in the position, after the 2/3/4th time...freeze them out and mean it...make them work extra hard for your time. Intially its a meeting, they come 50% and you come 50%...but after a few times of being tardy...you make them come most of the way in terms of effort to make it happen.