I had heard about the lost of smell and taste been part of Covid symptoms, my older daughter has a friend that caught COVID early on, I believe he was patient Zero in the County were he lives. He told the story to us via blog and it was not fun, he is an asthma sufferer so the virus wreck havoc on him, he has a 2 years old daughter and saw his grandfather before he got tested positive. He was so scared that his daughter and grandfather had caught it. He has now recovered but his lungs are not at full capacity. And at the very end when he thought that he was better he lost his sense of smell.
This virus is very tricky and scary, please keep safe and hopefully your SIL will recover soon.