This is a local dive for me/us. I have taught a bunch of OW classes here. Here is what the Park City Record quoted, "According to Wasatch County Fire District Battalion Chief R.L. Duke, the woman was taking a class when she began experiencing difficulty. Though she was able to surface, her troubles persisted, leading to cardiac arrest."
The first thing I did was check our shop schedule to see if it was one of our classes or anyone we know. It wasn't, but if there's anything to learn from this, the dive community here is definitely going to be interested to know the cause. The dive is very straight forward. A big 60 foot deep round hole, about 40 feet across with a platform on the side at 20 feet and a hanging PVC safety stop bar at 15 feet. Water temp right now is about 94 degrees (geothermal). DCS on one or two shallow OW dives is very unlikely, but an embolism, etc. wouldn't be. Of course, it could just be a medical issue as well.