Can they even see all possibly previously undetected health issues posthumously? I mean, say she had hypertension for some reason but never had it checked or diagnosed, would they be able to detect that necessarily?
Hypertension damages tissue, so there's a few things that are strong indicators of a person having been hypertensive. The size and weight of heart, or damage to the capillaries of the kidney. She'd definitely be an outlier if she had hypertension at that age though.
It was her aunt saying no underlying health issues, which obviously isn't the same thing. I suspect the autopsy will reveal something.