She’s in her sixties with two other health issues that make her high risk.
When her and my dad got COVID (from a careless neighbor who, despite feeling like he had the flu decided to make the Saturday afternoon neighborhood rounds and spent two hours in my parents living room talking) we ordered a pulse oximeter for them and made them swear that the first time it dropped below 90 they would go to the hospital.
She kept her promise and the doctors said that getting in early enough allowed the antibody cocktail, remdesivir, etc a better chance to be effective.