The difference, of course, is that had she died at the hands of a US physician her family would have had recourse and, in substantial part because US medical institutions are aware of the financial consequences of that recourse, they try really hard not to screw up.
Not really a fair comparison. Getting surgery in a quality US hospital, by a quality US surgeon is comparable to getting surgery by a quality US surgeon in a quality Mexican surgical facility.
It is not comparable with just hunting up someone who will do the surgery, wherever. The operable missing word is quality.
People can and do find unqualified or poor quality surgeons in the US as well, if their sole consideration is cost. Some are acting illegally, some not. Some who are qualified act without malpractice insurance and have no substantial assets to seize.