I have a thread with a very similar situation (Tips for trying to net a gal who is flakey) and Cinnamon's advice was to be blunt with her and give an SOI (Statement of Intent).
Quote:
Okay, flakes are easy to deal with.
Yes, you have to punish them, but not with stopping contact.
You need to punish her with our SOIs (Statement Of Intent).
Let her know, flat out that you want to hang out with her but you are a very busy man. Let her know, bluntly, that if you reserve a spot in that busy time for you and her, that she needs to show up. You have lots of other people (since she has low-ish self esteem I'd just keep it at people) you could be spending this time with, you have lots of other things you could be doing with this time. Sit her down and let her know that. Or, if she flakes on the talk, let her know.
Make it clear this is something you expect from all the people in your life, and if she wants to be one of them, it's something she'll have to do.
Trust me. Women appreciate and respect honest, open communication. If you communicate with her honestly and openly, what you say will be heard and respected.
Cinnamon
If she is still flakey, than she's not worth it.