Instead of morality, I think what Alice seeks here is deniability. If Alice does not take the test, she can convince herself (and possibly others?) that the probability of her sore throat indicating COVID is as low as she wants. No one else can really tell how bad it was—certainly not days later, when the thing is discovered—she may even claim that she felt nothing unusual. She is still immoral, but she can at least convince herself that she has done nothing wrong.
Doesn’t society already consider it immoral to go to crowded places untested when you suspect you have COVID? This is not just about a specific detail of this specific story—one important feature is morality is preventing humans from convincing themselves that the thing they want to do is the utilitarian choice. We decided that going untested is immoral precisely because people like Alice who avoid testing themselves for such reasons.
Instead of morality, I think what Alice seeks here is deniability. If Alice does not take the test, she can convince herself (and possibly others?) that the probability of her sore throat indicating COVID is as low as she wants. No one else can really tell how bad it was—certainly not days later, when the thing is discovered—she may even claim that she felt nothing unusual. She is still immoral, but she can at least convince herself that she has done nothing wrong.