If she were just gritting her teeth she would be pulling her lips back, not letting her cheeks go slack and jutting her lips out. They're basically bimbo lips.
I don't like this sort of subtle titillation. It's the same thing with the "Manga" image in the latest article--that image is clearly sexy, but it flies under the erotic radar by being excessively "cute". (*tee hee*)
I think if you're going for sexy, then go for it all the way in a more overtly erotic style, like oldschool Larry Elmore or Clyde Caldwell cheesecake. Otherwise just don't go for sexy at all.