I am a Girl Scout leader and have taken my girls on 2 Carnival cruises (this past August they were 13, and the prior cruise they were 11). When they were 11 we only had 5 girls and an adult ended up paying to come with each girl (not my choice, but the parents of the girls were hesitant to let them go). In August there were 5 girls and 2 adults, so we had an adult in each room, just because it wasn't possible to have 5 girls in a room, and we didn't want to have to raise money for an additional room. We have another trip planned for August 2011 to Disney World and are in the process of raising that money now (plane tickets are bought!) - again this will be 5 girls and 2 adults (the girls will share a room and the adults will be in a connecting/adjoining room).
You should know that it is encouraged by Girl Scouts (at least at my council) that girls have their own room. As long as the chaperones are in a room next door or across the hall, I'm not sure what the problem is with that. Before going on either of our cruises my girls had to agree to a long list of rules which included never being without a buddy (and of course lots of other safety rules - some specific to ships some just general safety, like never letting anyone in your room even if they work for the hotel/ship). I presented these rules in a contract form and made them and their parents sign it. My girls understood how seriously I took safety rules (with the "buddy" rule being right near the top), so I never had an issue with them breaking those rules.
My troop has always raised the money necessary for trips (2 cruises, 1 week at Disney). We have been asked the "educational" question alot. Everything about a trip is educational (if done the Girl Scout way). How to raise the money. How to plan/run the event/activity you decide on to raise the money. How to decide where to go. How to determine the cost of a trip. How to book. What to do where you are going (with the cruises we did there were 2 ports each, so research on each of those). For some of my girls it was their first time on a plane; first time to Florida, etc., so everything was "educational."
I'm surprised at how many of you are surprised Girl Scout council would approve these trips - this is what the girls are supposed to do. Learn and have experiences with their troop! At age 12 Girl Scouts are allowed to go on Girl Scout destinations (10 day trips to Europe), but they have to apply and show they have travel experience and experience away from their families. This was the #1 reason I wanted to book the first cruise my troop went on (although it didn't really work because each girl had an adult relative with her). If the girls want these "extra" experiences, they need to do some traveling as a troop first.
My concern with this proposed trip would be Mexico - what ports is the ship visiting? Are they safe? If it were a cruise to the Bahamas I would not have any problem saying yes she should go, the destination being the western side of Mexico just makes it all questionable.