I really like the whole vibe and look of the outfit, and her hair is amazing too, but I think this is really a matter of all the details working together. The color combo, the fit, and yes, the fact that she is slim and has a model-like narrow-hipped build all make it work. I actually think her long neck really contributes to the look too -- the popped collar wouldn't be nearly as successful otherwise, and that's a detail in styling that helps push this look up a notch.