I have always packed very simple, but elegant cocktail-like party dresses. I have a few "little black dresses" I like to bring, and I have never felt out of place wearing them. Some people go way out to get hair and make-up done, along with a very formal dress. I have also seen some people have utter disregard for the formal evening who show up in jeans and t-shirts (what irked me more is that they were allowed to stay in the dining room!). I think it is really up to her. If she doesn't go out and get dressed up very often, then it might be fun to go all out. As far as the men go, the past few cruises I've been on, I've seen a lot of men opting to wear nice suits, although you will spot a few in tuxes.