“”bobbing” in the water with a flotation device “
She had a defective flotation device designed for an infant, not for a woman weighing over 200 pounds, so she wouldn’t have been “bobbing”, she would have had to be treading water, and she apparently was not a good swimmer. Perhaps you have never had to tread water for any length of time, but it is strenuous exertion.
“surrounded by people who later reported that you were responsive and appeared “fine” to them”
She wasn’t surrounded by people. She had drifted away from the plane and was accompanied by only one coworker, who said she was clearly in distress before she stopped breathing, not that she was “fine”. You don’t have your facts straight.
“Is is statistically probable her death was natural given all the circumstances in play?”
Yes, an old overweight woman who is not a good swimmer having heart failure after a plane crash and having to tread water for an extended period of time is very statistically probable. It’s certainly infinitely more probable than the magical frogman assassin theory.