The person in the article we are talking about is a covid idiot to put it nicely. Every situation is different but common sense pertains to all the situations.
A 16 year old gets infected you basically quarantine him/her if space permits it.
I am unable to read the article - does the article say HOW she exposed her daughter?
Keeping a 16 year old quarantined is definitely reasonable, but most people here are told that their young children must stay home if
anyone in the house is in quarantine, even if not actually infected.
The reason is quite simple - unless the older person has a way to NEVER leave their room (even for food, restroom, etc) it is close to impossible to ensure that the younger children won't try to run over to them.
Seven and a half is old enough to understand, but young enough to not necessarily understand how careful they have to be. The question then becomes how much it is reasonable to make yourself crazy, since the vast majority of kids that age come through it just fine.