Normal
She would be overdressed in a gown. As far as how many men wear tuxes, it seems to vary by line, itinerary etc. Even though there will be some very underdressed, she will not be out of place in a formal gown on formal night. Plus she will have the added pleasure of knowing she is following the requested, suggested, encouraged dress code. By the way I plan to be in my tux on formal night.
