There's something about COVID that brings out the most bizarre attitudes in people. I don't know if it's a response to the lockdowns or what we all went through, but it's just bloody strange.
COVID can be extremely mild, and for many people it is.
However, it kills some people, and in others it seems to be producing longer-term disability. There's also some evidence that it's linked to damage to other organs.
It's not "just a cold", even if that's how you experienced it.
Totally understand that people are sick of hearing about it. But it's socially responsible to try and prevent infecting other people with contagious illnesses - and if there were readily available tests for other nasty viruses, I'd happily test for those too.
We're having building work done. My DM caught COVID off one of the builders and it infected the whole family, including my two SEN DC (one of whom is profoundly disabled). It actually shocked me how literally everyone who walked through that room on the same day ended up with COVID (including two other unrelated contractors from another firm who visited later in the day). I knew it was contagious but I was in the room for just a few minutes, and not even at the same time as the infected builder! It's a very contagious virus.
DM ended up in hospital on the COVID ward, unable to breathe despite being put on oxygen. It was fucking terrifying and completely out of the blue. This was a couple of months ago and luckily she's OK now but my stepdad is suffering from an unpleasant labyrinthitis since COVID that he can't shake (and has caused him to fall).
I completely agree that the OP's DD should still do her exams - she's well with no symptoms.
But all this head-scratching about why people are being cautious around COVID - there are very good reasons. Luckily we know more about it now and it's not quite as scary as we first thought, but it's still a deeply unpleasant virus for some and can have serious consequences. Why are we pretending this isn't the case?