She was never over the top with anything, but she'd typically be showing the most skin in the room.
One time, we were at dinner with her parents and she chooses really high heels and a very short dress.
However, she can display her figure and best features in a non-slutty way as well, not the way you seem to describe.
Like Rob Banks said, it depends how serious the relationship is.
However, I think we are forgetting a good reason to actually encourage your casual girls to dress sexy as hell: social proof.
Showing that you are with the hottest, sexiest girl in the place will impress both men and women in any given venue.
All of this naturally presumes that the girl is an 8 or better. But a girl doesn't have to go overboard in order to show how hot she is.
There are outfits that draw attention without making the girl look like she charges by the hour.
Those shorts that show off half her ass and that basically see through top she wears with no bra, that's slutty.
While she may, as many have pointed out, be advertising her own goods, she is also advertising your status as an unintended consequence.
All of this naturally presumes that the girl is an 8 or better.
Think about it this way: If you've already seen her naked, then you already know what her body looks like.
There is no need for her to dress revealingly for you, since you already know what she looks like naked.