First thought:
Second thought, if you're really into meeting this chick, and she's free this week
as she says:
Don't message back immediately. Let the hamster spin.
Follow up in a few hours, tell her that you've got a lot going on this week..
You: "When are you available ?"
Her: "(Gives a night she can hang.)"
You: "Any other night work for you ?"
Her; "I can do ______ night, too."
You: "Cool, I'll be at X around X time. Come through."
Whatever night she throws out first, you can't make it (no reason to tell her why). Let her offer up a second night, that will help give you an idea of interest.
While I'm not advocating trying to 'figure her out' or anything close to that, some situations take precedence over meeting up with someone (think sick or dying relative). Her being available/free all week might be her way of saying she knows she flaked. Those flakes could have very well been legitimate and out of her control. But she still wants to meet up.
I had a situation myself, had a sick parent that (of course) took priority over a potential bang. I'm sure a few women in the pipeline figured I was nothing more than a message/text guy, a few more were cool with meeting up a week or so later. Once we met up, the inevitable "I thought you were one of those guys that just wants to message" conversation comes up, and I'll tell them about the sick parent.
All that said, have a backup plan, as always. If she shows, great. If not, no loss.
After that, if she doesn't show, next her.