There's a girl at our school who makes us very angry?

Ok, there's a girl at our school who thinks she is the best. She thinks that everyone likes her and thinks that she's good at her studies. And today,at out computer test, nobody learned cause itz super hard :P. And usually at out computer test we cheat :P. So, today 3 of our friends planned to keep the book under our desk, when i was cheating from the book. She saw and told to sir but luckily i hurriedly took the book out of my desk while nobody saw, i kept it in my bag. And last year she bought a page and cheated the whole test. She got very good marks by cheating and when i saw her cheating,i didn't told to sir about this. She makes me sooooooooo mad and my friends too. What should i do?. Thanks!