ok first of all if you dont have any classes with her and you are so gameless that you are asking online for help, then i say forget it and dont embarrass yourself. You would have to be an extreme pimp and a really good talker to just get a random girl like that that probably has never even seen you before in highschool, where there are cliques and everyone basically knows each other. she probably has a lot of friends so if a random kid she doesnt know comes up to her and starts talking, that will be really wierd to her and probably creep her out. Trust me I thought about doing the same thing you are thinking about doing but it just wont work in highschool, but in a couple of weeks you will just forget about it and go find some other chick.
But if you are still horny for her then I suggest doing something like this: find something she does like a club or a sport, or if you stand next to her in the cafeteria line, whatever the fuck i dont care. And talk about it. If you have a hard time thinking about what to talk about then forget getting any girls and go practice with friends. But you should find that one thing she does and just start talking, like if there is some shit cafeteria food start talking to her about how shitty it is. Or if there is a club or a sport, start talking about that. Talk smooth, no stuttering or making it seem like you are having a hard time making shit up. And most importantly, make it funny, make the conversation interesting and if you can make her laugh or put a smile on her face, you made it. Oh and smile yourself, dont look like a dull faggot. After a bunch of these little convo's, if she still hasnt opened up to you or went beyond the short talk, then stop starting the convos with her. Pretend to ignore her. You say shes hot so i guess she gets a lot of attention, and you gave her attention and now took it away and she might feel that and want the attention back. If it works and she starts talking to you after that, then great shes interested in you and try to talk about deeper things, then it will just get bigger from there. If she doesnt start talking to you after that, then whatever, she doesnt want you and you cant do anything about it, there are 4 billion fucking women on this planet so dont cry about 1.
But im assuming from you going online asking for help that you arent capable of doing the above, so i suggest you go practice with friends and try to talk more eloquently and try to be funnier and smoother.
Aite good luck man, i hope this helps.