It seems interesting that (apparently) nobody drilled into the boat captain about his statement that after 4 minutes, he assumed she was dead.
She was found with a full tank. The boat captain and crew would surely have known she had a full tank. So, assuming she was dead after 4 minutes seems highly specious.
I didn't see any mention of an analysis of the gas in her cylinder. Did I miss that? I also didn't see mention of an autopsy to verify cause of death? I only saw statements that she had no underlying health conditions that would explain her sudden death. Could she have been poisoned? Died of CO poisoning?
Or as simple as she went down with her air turned off (whether on purpose or by accident), drowned, they went down and got her and realized (or knew?) what happened, and then decided to collude in opening her tank valve and dropping her back in, so as to avoid being blamed for sending her down with a closed tank?