As for the friend, it would depend on when you cruise. If its during a school break (summer, holiday, etc) then she probably would have no problems finding someone her own age on board. If not, and you can swing it, bringing a friend along might be nice as well. Just remember they will be together 24/7 for however long the cruise is and girls can get into it with other girls. Be sure shes a really good friend and you can stand to be around her as well (I know, terrible to say, but its something to consider). My parents used to bring a friend along for my brother. Long story short, it got to be pretty bad after a few days! You might consider just the two of you going for some bonding time (if you dont see her often). Do some fun excursions together, etc. Those would be the times I remembered most when I was older!