Oh gosh my sister was like that, but believe me the extrovert in her was mostly an act. Now as an adult she still does it but I know that deep down she is really quite unconfident. She's just a better actor than you and me.
The first thing to do is to try as hard as you can not to let her behaviour affect you. If you can, just laugh it off. Think about out it, why would she want to be friends with your friends? Answer, because she wants what you have. Ignore her, dont be jealous, turn your head and look away. Concentrate on being good at what you are good at and stop thinking about her, or comparing yourself to her.