Honestly it sounds like she may just be kind of a flaky person. I'd try texting her a bit, make some small talk, joke around etc... That could kick the sparks back up potentially and have her more motivated to see you.
If all else fails use the nickname game. I wouldn't use it unless you haven't been able to get her to hang out with you for at least 2-3 weeks. You just send a text or something and tell her you thought of an awesome nickname for her. When she asks what it is say something like "Oh it's way to good to tell you over text, I'll have to tell you in person :-p". Curiosity killed that cat as they say
