Where can you get a cute, but dressy romper or dress?

We have to go to a wedding in the summer. My 13 year old daughter wants to wear a romper (she is girly, but not into dresses), but I don't think there are dressy rompers. Men have to wear sport jackets, nice pants, and a tie. What dresses (casual,but fancy) or rompers are nice? LINKS or store names please! Thanks!