I worked with both Jennifer and the missing Bahamian man, Mark Gibson, at the field station on Andros Island and was with them up to just a few weeks before they went missing. As they were both my co-workers and my friends, maybe I can offer some information that can clear up a few of the details for you.
Mark and Jenny were both very experienced divers and very familiar with the environment they were diving that day. Mark was a diver master who was native to Andros. He was an exceedingly kind person and excellent teacher. Jenny researched blue holes and was well aware of the conditions there. They both took safety very seriously.
When they didn't return back to the field station as expected, extensive searches took place but the only sign ever found was the boat they had taken out that day.
There are many dangerous things that can happen while diving and blue holes have some unique characteristics that can add extra hazards. That particular spot has a strong current and many cave areas where someone could get stuck. There could have been an equipment malfunction or a health situation like nitrogen narcosis. Neither would have left the other behind without trying everything to save them and most people assume that that is what happened in some manner
The show Expedition X has an episode where they discuss this case, though not by name. Season 5 episode 7 - The Beast of Andros Island. They discuss 2 divers going missing and dive King Kong.
Like many disappearances, there was some wild speculation like them perhaps running off together. They both had families they loved dearly and a purposeful disappearance would have been completely unnecessary. Unfortunately diving accidents happen, and this one left many people missing these 2 great people.
Please let me know if you have any other questions I might be able to help with.