1. Low oxygen would kill anyone, but that would be very unsual.
2. The stress can cause such an event to happen, especially in the setting of structural heart disease which may also be associated with various channelopathies that could predispose her to SCD. Fruthermore, if her diet lacked certain nutrients that would also predispose her to SCD.
3. It's probably one of the best ways to go.
4. MVP has a small association with sudden cardiac death. It's not very strong but the signal is definitely stronger than that of the general population. The problem with this is that there may be other conditions that we are just beginning to learn such as long QT syndrome, ARVD, HCM (unlikely here because of the autopsy findings), Brugada's syndrome or CPVT which may exist in the background and be the actual cause of death. The current recommendation is for MVP patients to be on beta blockers.
5. See #4. Again, this is an association, not a cause and effect relationship because we just don't know enough. I would say that any of the other conditions that I mentioned are more likely to have caused her SCD.
This is a very interesting question to ponder? I sympathize for the lost, it is even greater in the lost of a young life in its prime to never to fullfill their ambitions, but such are unfortunate events in life that we can never comprehend.