Diantha is the most fabulous Pokémon champion I've seen. From her outfit, to her attitude, and her battle theme, everything screams "BITCH I'M SO FABULOUS". And I just...couldn't resist. I'm sorry.
I suggest you to listen to her battle theme while looking at this picture, I really used it to catch Diantha's attitude : http://www.youtube.com/watch?v=XoM8wGIrF8k