Those life jackets are only designed to keep one’s head above water. C A could very well have occured, making her unconscious at which point she would not have been able to hold her head back and keep the water from entering her mouth......
And Wikipedia says, "In most persons, the laryngospasm relaxes some time after unconsciousness and water can enter the lungs causing a "wet drowning". However, about 710% of people maintain this seal until cardiac arrest. This was called "dry drowning", as no water enters the lungs. In forensic pathology, water in the lungs indicates that the person was still alive at the point of submersion. Absence of water in the lungs may be either a dry drowning or indicates a death before submersion."
Given all that uncertainty, I don't think the writer of the original article has enough information to draw the conclusions she does.