I know your talking from experience, but we cant just sit here and make assumptions.
You're doing the same thing by assuming she's serious on NO experience at all.
Final word, let her be, if she's lying then she's a liar and just wants your attention.
If she's serious, which I still seriously doubt she is, you did nothing wrong from what you've said, and no one is to blame.
I've driven to my friend's house in the past because of threats like this only to find her watching TV.