Two Women Fell Sick From the Coronavirus. One Survived.

[Laelth]

11. This virus can trigger a "cytokine storm" that will kill some people with healthy immune systems.

While it's true that the percentage of elderly and compromised people who may not survive COVID-19 will be higher, the raw number of fatalities will be higher among those with very healthy immune systems that can be triggered by a self-destructive cytokine storm. At least, this appears to have been the case with the 1918 Spanish Flu epidemic, and it's the most likely cause of death in the case of the woman mentioned in the OP.

It is believed that cytokine storms were responsible for the disproportionate number of healthy young adult deaths during the 1918 influenza pandemic, which killed 50 to 100 million people.[15] In this case, a healthy immune system may have been a liability rather than an asset. Preliminary research results from Hong Kong also indicated this as the probable reason for many deaths during the SARS epidemic in 2003.[16] Human deaths from the bird flu H5N1 usually involve cytokine storms as well.[17] Cytokine storm has also been implicated in hantavirus pulmonary syndrome.[18]

https://en.wikipedia.org/wiki/Cytokine_release_syndrome

-Laelth