It appears that she is mightily offended that people are calling out the WaPo for publishing fake news (the non-existent Vermont Power hack) just because they, well, you know, published fake news.
She thinks that the term has, "Had its 15 minutes of fame."
Let's be clear: If you have an anonymous source, and they burn you repeatedly, and you don't burn the source, and you keep going back to the well for more quotes from them, as the Post has done with the US state security apparatus since its founding (with a few notable exceptions), it's fake news.
Use the same standards as libel for public figures: A reckless disregard for the truth, and a quick Google gives us this
Disregard of the truth or falsity of a defamatory statement by a person who is highly aware of its probable falsity or entertains serious doubts about its truth or when there are obvious reasons to doubt the veracity and accuracy of a source [the knowingly false statement and the false statement made with reckless disregard of the truth , do not enjoy constitutional protection "Garrison v. Louisiana , 379 U.S. 64 (1964)"The Washington Post is not just regularly burnt by its sources in intelligence, it is routinely burnt by these sources.
The reporters know this, the editors know this, and Margaret Sullivan knows this, and they just don't care.
This is the very epitome of fake news.
*This is a reference to Mandy Rice-Davies and the Profumo Affair, who when told that Lord Astor denied having ever met her, much less f%$#ed her, replied with a rather similar quote.