My thinking exactly. Probably did it anonymously so there would be no chance on anyone ever connecting her to the sample she provided.
If it were true she would be rubbing everyone's noses in it. But it isn't so she has to hide.
How hard is it to get a surreptitious sample?
Run up and grab a soda can, or a drinking straw, that she has drunk from. She’d sh!t herself, and have her well armed security detail do anything, including kill you, to keep it from being taken. Bet on it.