My DS (9) went on the Pirate Cruise July 8th and had a BLAST!
Don't worry about your DD . . .each child who doesn't have a sibling or friend will get paired up with another child . . .my DS was paired up with a 10 year old girl! They were instructed to "hold hands" the entire journey . . .it's a good way for kids to meet . . .I'm sure you DD will have a great time!
Have a GREAT trip!