I'm Grade 8.. She's my friend, and I always get jealous of her.. Yeah, she's dumb. And I'm smart. But, she's beautiful, sexy, rich and sooo PERFECT, she always gets what she wants, she has nice clothes and shoes.. My crush also has a crush on her.. :'( What should I do?

You are smart. Use your brains and realize that brains will carry you through life with a lot more freedom and benefits than her lack of them, She won't always have her parents either, to give her everything she wants.

We all experience jealousy. But we can curb it. We curb it by adopting a philosophy of 'this is the way life is, and we can't always get what we want, and it's not necessarily good for us anyway.' (Actually the word you want is envy, but for some reason people use jealousy for both concepts.) We curb it as a means to an end - in your case, the end is to keep the friendship. If you are willing to lose her as a friend, then drop her.

Get over it.
If she is your friend look at her in terms of the kind of friend she is to you rather than the things she has or stop being friends. You make be jealous and smart but you are not a good friend if you're calling her dumb, if you are only pretending to like her. She may think you are the greatest.