The surgery was minor and cosmetic. She was cremated without the concurrence of her husband.
So I would assume she went down there looking for a Mexican doctor, maybe found a legitimate one, or not, and he botched the procedure, or she had an unexpected, severe reaction to the anesthetic. And he was not equipped to handle a cardiopulmonary emergency.
You don’t have to go to Mexico for that to happen to you. It happens in both Texas and Florida at intervals.