Unfortunately you can't judge until you meet her, she could be busy or she is trying to make sure you are not a grade A clinger prior meeting. Just set up a date to meet her in person and see how it goes.
If she is hot like you describe she probably have very high standard and is very picky that's why she is single
If you've never met , I 'd assume she's just being guarded. I am too with people I haven't met in person. Well, until I get to know them more. If you're open and reveal emotion to her she may do the same , in time