My understanding is that Alysa had two negative tests before leaving for Nashville. Daily tests weren't being conducted in the bubble, however I think they were testing everyone going into the rink today. It's possible that the positive was recorded there. It's also possible Alysa had symptoms and then got tested. If there were any symptoms, they sound like they are mild. I am very glad to hear Alysa is feeling OK mentally and physically.
We have a month until the Olympics, more than enough time to get a negative test. I'm guessing you need to test negative up to two weeks before entering China, which in this situation would be entirely possible.