Well tiger sharks are rare all over the world, and basically super rare in Cozumel, are there any there? Possible, if they are where? Likely outside the dive sites as there is so much diving activity that anything that is there even rarely there ends up getting spotted sooner or later.
If marine life ate her down to bones it's likely that the body didn't float after the death but sank to the bottom, dead bodies bloat and float so her weights would have had to over compensated for the bloat. Likely she was well weighted or over weighted, had either a medical incident that resulted in her drowning and sinking, or a tragic series of events with equipment that overcame her and drowned her and she sank. Where the body or parts ended up could be anywhere within miles of the incident due to the currents, Cozumel is a drift diving area so the water is always moving. Her head being removed is pretty plausible since a diver in a wet suit has a wet suit that is holding the main parts of the body together, the hands, feet and head are exposed.
What I'm saying could have nothing to do with reality, but when there is a dive accident it's usually more mundane and simple than dramatic like a shark attacking a diver on the surface which is extremely rare to the point of statistically an anomaly. Did a shark of some sort have something to do with dismembering her dead body? That's much more likely, but who knows. I'd personally look to something much less rare and dramatic and at things that are more likely to have happened. The amount of live divers attacked and killed by sharks is pretty tiny.
