I know everyone wants to claim it was here in December, but don't you find it a bit coincidental that she met with a nurse in February that was working at the infamous nursing home in Kirkland, right as they were about to have their huge outbreak? Having antibodies doesn't mean that she had Covid-19 in December, because there are so many asymptomatic cases. Also, it would be very unusual for her to have a highly symptomatic case of the disease in December and not infect anyone around her. This would be amazing to me if true. Unfortunately, there is no way to prove it, and lots of reasons why it could be just coincidence.
Also there is this from the article: 'Genetic sequencing of multiple cases from the Western Washington outbreak by Nextstrain, an open-source genome data project, further indicates “there is not a lot of support for an earlier, independent event,” Roach said.'
So yeah, it's possible, but not likely at all, in my opinion, that the virus was here in December.