Tragic news but i wish the BBC wouldn't contradict themselves in the article:
"We found her face down, she was unconscious. She had her buoyancy aid on, it was keeping her afloat but it wasn't keeping her head out the water.
"So we understand that the six would have required to be wearing life jackets but there is no indication yet of exactly what happened."
So which one is it? Life jackets by their very design have a collar on to keep your face out of the water, buoyancy aids do not. It does however highlight the importance of having knowledge of what you are sailing/floating on especially if the water is tidal.