If you are infected, and it's early, you should be able to get an antibody cocktail now. This looks like it really helps, and it gives you about three months of passive immunity. It's not cheap, but the government pays for it, so it should be free for patients.

It's FAR FAR cheaper than them paying for a month in the ICU.

And yes, your sister had Covid-19. Loss of taste and smell is a very common symptom. And it's almost impossible to live with somebody infected and not get infected yourself. That includes kids, parents, and grandparents.