Please help. Did my mom die of a heart attack?!

Please help. Did my mom die of a heart attack?

A week ago my mom passed away very suddenly. We did not do an autopsy as we know she died of natural causes. But the family is wondering wether it was a heart attack or something else such as a massive stroke, heat stroke, or an anyurism.
The facts:
She had been out in the garden weeding for most of the day. The weather was 95 degrees and humidity was high. She came in around 6 pm and said she was tired and had a heartburn so she took some antacids and went to lay down. at 6:30 she got up and said she felt better. At 7 pm the lights went out due to a thunderstorm. While the lights were out she lost her bowels. She agreed to go to the ER, but wanted to shower first due to being soiled from losing her bowels. They came on at 7:30. She then took and shower and dressed herself. The neighbor came to take her to the ER. She got in the car and buckled her seat belt. Immediately she passed out. She was breating with a pulse for about 5 min. before dying.
What caused her death?

First of all accept my heartfelt condolences on the sad demise of your mother death, may her soul rest in eternal peace .
I am sorry to write that your died of Acute Massive Infarction of heart.
Was she hypertensive or diabetic or both? Such incidences are common in hot weather, as a precipitating factor.