So you never met this girl before?
And then when the two of you did meet each other, she seemed to lose interest?
Well, that's simple; there just wasn't any chemistry there. No spark.
Sometimes you have an interest in someone that you have only spoken to and never met. You have to meet them to figure out whether or not you are physically attracted to them, or whether or not there is chemistry.
So she thought that she might be interested in you romantically, but when she finally met you, she didn;t feel any kind of attraction to you.
Sorry, but it happens sometimes.
You should probably move on.
You aren't going to get anywhere with this girl outside of just friendship.