Interresting to hear this... When I was on the Mediterranea, I spoke with waiter who was on the Magica when it happened. What he told me is that some older people were giving her alchool and she got quite rowdy. She started threatening she would jump out and no one beleived her due to her state of mind.
She jumped out, hit her head on a lifeboat. In the morning, they found her blood on the boat but it was already too late.
He told me that it is very easy for kids to get access to alchool onboard. They just become friends with someone older that gets them drinks on a stolen SeaPass... I guess it's a problem that is not just on Costa's ships but all of them. The SeaPasses should have pictures of all passengers and their age. This would avoid a lot problems.