Originally Posted by Saulbadguy
To answer your question (THE FIRST HIT IN GOOGLE WHEN YOU TYPE IN PASSPORT CARD VS PASSPORT BOOK):
You only really need a card.
On a cruise you are advised to put your passports in your safe. They sell novelty stamps in the port but you don't want to risk losing it. Supposedly you can take the book to guest services and they will stamp it for you at each port.
Did you mean to say you need the book? I don't see any reason to get a card for a cruise - especially since she wouldn't be able to use it for any other travel in the future.