I wish my girlfriend would dress like my brothers gf.
Why do you want to tell your girlfriend what to wear?
My brother's girlfriend wears beautiful and sexy outfits to show her body off.
It's wrong to act so controlling. If you're so shallow about what your girlfriend wears, you should break up with her so she can find someone who respects her.
I'll tell her to change.
It is wrong to try and change someone's style and clothing to show them off. If you want you can try to buy her an outfit and see if she likes it or not. She should not feel forced into doing anything.