Did Miller just tell half the story?

I haven't written about this yet because everyone knows she testified today, but we didn't know much about it. Now we know that Cheney's lieutenant 'Scooter' Libby leaked Valerie Plame's name to her. But apparently she's got another name that's staying secret. Or to put it in Rumsfeldese, their are a few known unknowns involved:

If anything substantive came out of Miller's brief appearance before the press, it was this: She emphasized, at least twice, that there had been not one but two prerequisites to her testifying before the grand jury. First, Miller said, she needed a personal and voluntary waiver from the source she was protecting -- a source the New York Times and the Washington Post have both identified as Libby, Dick Cheney's chief of staff. Second, Miller said, she needed an assurance from Fitzgerald that her testimony to the grand jury would be limited to her conversations with Libby -- which is to say that it would not require her to give up the identity of any other sources she might be protecting.

Miller said Fitzgerald's agreement to limit her testimony was "very important to me," and that she would have stayed in jail "even longer" if she hadn't gotten both her source's waiver and Fitzgerald's agreement not ask about other sources. "I could not have testified without both of them," she said.

So one question has been answered today: Libby, it seems clear, was the source Miller was protecting. But who is the source she's protecting now?

Why she'd be so committed to protecting someone who played her for a sucker (a la her gullibility on WMDs prior to the invastion) is beyond me.