I agree. If she was murdered, the killer was on the plane. If not the pilot (who had to be part of the plan to ditch the plane) then the passenger list needs to be checked very, very carefully.
Means. Multiple. arrhythmia induced through drug, stress or exertion, or other event appearing to be a heart problem, in tropical heat (at the destination), remote from facilities which are capable of giving critical cardiac care.
Opportunity: Improved by having high stress event en route.
It would have to be someone who would be close to the target normally on a regular basis or not appear abnormal to be there, and someone professional enough to use the opportunity.
An alternate possibility is that someone was hedging their bet and saw the entire compliment on board as expendable, fully expecting a significantly worse landing.