Am I Crazy or is She?

I bought tickets to a concert a month ago. My date canceled on me so I started asking around. I happened to post an invitation on a friends Facebook wall asking her if she can make it. One of her friends indicated she is a fan of the band so I invited her to join me. I had never met or talked to her before but the show was a month out and we agreed to talk regularly to reduce the awkwardness when we finally meet. We chat online for a little while most evenings and occasionally text each other. The show is now 5 nights away and I have a little bit of an issue. My date has recently starting acting kind of needy and possessive. She gets mad when I don't talk to her for half a day and keeps telling me she misses me, she gets vindictive when I tell her I'm going clubbing with friends, and what was flirting for fun now seems to have a more serious vibe to it coming from her. Our mutual friend has known and worked with this girl for years and told me she is a little weird but sane and reasonable. I don't know how to approach her about her bothersome actions without feeling like it will ruin the fun and anticipation of the show. I admit I've contributed to the situation but only after she claimed her actions are in good fun. I even had a phone conversation with her to directly state I have absolutely no intention of any activities other than enjoying a good rock show with her. She was relieved (on the phone anyway) by that statement but the next day is when the weird stuff started. I have a feeling it's a case of her being a little delusional and unreasonable about her and I for some reason, but she will deny it if I call her on it (but she will be upset secretly). It's too late to cancel with her and find another date. She already took vacation time that can't be revoked and I'm working with an intuitive gut-feeling, not absolute evidence. Suggestions? Thanks!