They do say smart casual, she could wear dress trousers and top, or cocktail dresses look nice. Make the effort on formal nights. The ammount of formal nights should be on your tickets/info, however if in doubt-ask your agents.
On a seven day cruise there are two formal nights, when men must wear a suit and a tie and women wear cocktail dresses. There are two other nights when men wear a jacket or blazar and a tie. Finally three smart casual nights when men can have an open necked shirt. Do not be worried about dressing for dinner. Everyone makes an effort, and they really are lovely occasions.
Enjoy your cruise. Coli.
Thanks very much for the help, I am looking forward to the crossing. Keit.