Actually baffled by some of these responses, I definitely don’t think you’re being unreasonable, OP.
Had a similar situation with my DM who we’ve bubbled with, a few months ago when pubs were open. She had seen a friend for a drink (well distanced apparently) and then had been to our house to visit my then 1yo DD, before announcing a few days ago that said friend hadn’t been feeling well. Turns out they both had Covid, though thankfully didn’t pass it to us.
I was, although concerned for them both, pretty annoyed that she hadn’t mentioned that to us before visiting. Bubble or not, I see no reason why that means we lose all common courtesy and would risk spreading such an illness to our family. I’d feel the same if it was any other contagious illness.
And as far as symptoms go, surely we all know by now that the variance is absolutely huge? DM had no temperature, a mild cough for a day or so in the middle of it, and though she did lose her sense of smell, this was around 2 weeks after symptoms had started and it came back very quickly, so with such a potentially serious illness, why risk it?