It is very sad that this happened but the presence of a lifeguard would probably have done no good anyway.
I think it was two years ago that I saw a VERY heavyset woman who was walking with two canes walking into the water on Divi Little Bay. Now usually the water there is quite tranquil but not that day. There was a red flag warning people to stay out of the water.
My husband and I felt quite good about going into the water even with the big waves. But watching her walk in you could predict what was going to happen. She fell over and it took several big men to get her out of the water and she got swamped many times.
Now, should the guys in Aquamania have stopped her? In my opinion, I think she would have said she was just fine to go into the water. She was from a cruise ship too so not staying on the resort.
It's your own responsibility to know whether you should be in the water or not.