I'd suggest not replying and talking to her in school -- unfortunately some people are much more comfortable over the internet than in real life, so from online chats their game looks amazing. However, when you finally hang out with the girl in real life, you'll look like a chode.
As for what to say, that's what canned routines are for!

Any story or DHV routine will suffice. When she asks you what you're up to, always appear busy -- remember to be flipping as many attraction switches as possible.
Good luck bro.