A single-light portrait

The umbrella was a 1970-ish Reflectasol.

The light and colors are great, the model is beautiful... Could be really nice, but this unnatural "studio smile"... :( What if you frame it like an old-fashioned high-school-graduate portrait (an oval vignette?), will it become appropriate?

Smile seems okay, but the lighting seems a bit too harsh to me. I don't like the shadow behind her.