I don't have any topics to talk to her about. But, I have talked with her online at great length.
While I have no idea what you have talked with her about online, I wonder that it never included any topics.
I assume you have hobbies and things that greatly interest you - I bet she does too. Do you know what any of her interests are? Have you shared any of yours with hers? Do you know yet if you and she have any interests in common?
Being told you are interesting is usually quite flattering. It's a bit creepy to have a stranger walk up to you and say "You fascinate me, and I'd really like to get to know you better, would you tell me some things about yourself?", but something along those lines can happen between people that interact at least a little.
After you talk with her for a short time, say goodbye with something like, "Thanks for talking to me today. I always feel better when I see you smile." Or whatever seems right/is true for you. You can ask her outright if she'd like to spend time with you after school, but you know her better than we do - and without knowing her at all, we have no idea if it's time to say something like that.
Interact with her and show you enjoy doing so. People usually enjoy that.
As to the friend, I don't know how good or mature a friend he is; he sounds possibly less mature from your description (volume and ego do not gaurentee that though). You again know him better than we do; good, real friendships allow you and the other person to honestly talk about things with each other. You can tell each other what bugs you about the other; and sometimes the other person actually tries to be reasonable when they realize they were not being so before. That friend might even make it easier for you to talk to the girl, because he sounds like he's not hesitating to talk to her, so be involved in the conversation too, maybe?
There's so many details we don't know, it's really hard to give appropriate advice.
But it's OK to be you, and to feel the way you do, and 99/100 times it all works out pretty good after a while. Good luck and keep figuring out how you and your life works!