I think the real point is that nowhere in the account of this accident is there any mention of something having happened that ought to kill a diver who is appropriately trained and experienced to do a sub 300-foot dive. Such a diver should have a VERY broad range of capacities, including staying calm, focused and rational in the face of almost any "normal" problem. Certainly, such a diver should not irretrievably lose buoyancy control during a gas switch -- even at 20 feet, where buoyancy is much harder.
Lack of experience almost certainly played a role. A diver attempting a dive with which she did not feel comfortable also almost certainly played a role. We don't know anything, really, about her training -- I have, for example, seen tech instructors here in Puget Sound allow their students to do their ascents while hanging onto a fixed line, which certainly doesn't measure their ability to perform if, for any reason, they are deprived of that crutch. I have no idea how much "scenario-based" training she had (coping with staged problems in shallow water) or how well she did with it.
I'm a fairly weak OW technical diver, and I know it, so I keep my dives relatively shallow and if I'm not comfortable once I get there, I say so. This is important for ALL divers, from the person with a shiny new OW card, to the person with full trimix or full cave. It's one thing to be a little apprehensive about doing a "bigger" dive, before it happens; but if once you get there, you can't settle and enjoy the dive, get out. I can't remember who said it, but there is nothing down there worth dying for.