Fun possibility – I’d never thought of this:
Miller doesn’t want to reveal her "source" at the White House – because she was the source. Sure, she first got the info from someone else, and the odds are she wasn’t the only one who clued in Libby and/or Rove (the State Dept. memo likely played a role too)… but, in this scenario, Miller certainly wasn’t an innocent writer caught up in the whirl of history. She had a starring role in it. This also explains why Miller never wrote a story about Plame, because her goal wasn’t to write a story, but to get out the story that cast doubts on Wilson’s motives. Which Novak did.