Well, Novak never said she was 'undercover.' I think that honor went to the NY Times and Washington Post - [Pincus?], who implied they got that from reading Novak's article even though it wasn't in there.
I think Newsday was the first publication to call her undercover...I'm not 100% positive, but that's what I'm recalling.
My mistake, as cyncooper pointed out it was Newsday.