What gas were they using? 32%? If caught in a down current what is the potential depth she could have been carried to in that particular site?
If, as a surface swimmer, you get caught in a rip current, you should not fight the current directly. You will lose that way.
Speculation: She saw the team separation and started to work against it. Hard. As her depth increased, so did narcosis effects exacerbated by the exertion and the excess CO2 it generated. Narcosis caused a narrow focus on a single objective that blinded her to other dangers. We know she was a big advocate of team diving. Focused on reuniting with the team, she unknowingly obviates the dangerous over exertion for a 61 year old heart. She fails to recognize that now the immediacy has shifted away from getting back to your team, to controlling your heart rate and your depth. At this point the immediacy should be to ascend, hopefully without getting arterial gas embolism. The incident spiral is already fully engaged and she may not be aware of it.
I have enormous respect for her. It is not easy to write the above speculation. But it is my interpretation of what she would have like us to be doing now. My speculation can well be the furthest thing away from what really happened. But I believe it was her wish that we explore plausible scenarios and try to learn from them.