Eleven years ago, while on our honeymoon in Cancun, I took my wife scuba diving and snorkelling as well. The snorkelling event was part of a tour through the mangroves each couple using their own little "speed boats". You would take the boats outside of the mangroves and then you would go out snorkelling in open water at a depth of 12' to 15'. I was aggravated by the fact that the guides forced us to use flotation vests. What is the point of snorkelling if you can't descend!? I wore my vest to get through the guides and into the water. Once there I gave mine to my wife and got to snorkelling the way it should be. At the time I thought the idea of a snorkelling vest was ludicrous and if you need to have one, you should only get exposed to water in the shower and nowhere else -- beware of tubs, they can also be dangerous.
This lady was wearing a noodle and a wetsuit and apparently no weights. She was in a guided group with several people close enough to signal audibly and visually. People thought she was fine until they had to go over to touch her. I'm having a hard time trying to imagine a "safer" set of conditions. What else could be done? Hook tourists to a complete set of remotely monitored biometric sensors? Maybe we should just stay in a couch and watch video gathered through ROVs because getting in the water is dangerous.
With all due respect to the deceased (may she rest in peace), we're all going to croak up sooner or later. Being healthy is simply dying at the slowest rate possible. It seems that it was just her turn. Apparently she died a peaceful death, or at least one where no one close by noticed any signs of distress or struggle. I can think of many more less than pleasant ways to depart from this world.