I would imagine it is difficult to ascertain actual cause of death when more than one life threatening cause exists.
There is the synergistic effect that both kill more effectively together than when acting independently. In this case I suspect difference in reporting cause of death is open to interpretation.
It's literally not open to interpretation. She had a heart attack. that's it.
The person at the morgue heard she had a cough so wrote down coronavirus as a cause. No one in her family reported she had any signs of coronavirus except a mild cough before that. She hadn't been I'll with coronavirus.