If she just quietly conked out and died or after feeling a little sick, I'd be inclined to think of a blood clot that broke off and got to the lungs or brain. This has happened plenty of times in younger women. We don't have enough details as to whether this was the case, or whether she showed outward signs of some kind of extreme distress, seizures, etc. I'm not automatically jumping to the stereotypical conclusion she was a drug mule. One could just as easily use an alternative theory based on stereotypes that she flew long haul too soon after having plastic surgery.

I'm also a little surprised that if she was pronounced on board while near IAH, that they just didn't travel on to DFW with priority clearance for landing. At that point, there was nothing anyone could do even if she did get to a Houston hospital.