Megan
The question you're avoiding is:
Would the dog have died if it hadn't been placed in a minimally ventilation overhead? Something the FA improperly and in violation of the rules of carriage forced the woman to do?
Ok, the dog breed in question doesn't breath very well - something that placing it sealed inside a minimally ventilated overhead almost certainly made considerably worse.
BTW, just returned from a ski vacation in Breckenridge - altitude 9,600 ft. Pet dogs are very common there - and I saw a couple bulldogs during our visit.