If she never wrote about Plame, then wouldn't it have to be "concerning Iraqi efforts to obtain uranium"? She was the Times' "beat writer" on WMD, after all.
In order to have a "source", one must first have a story published, I would think. Indeed, to warrant the GJ subpoena, one would've had to have published a story in which one cited a source. I doubt they can subpoena idle gossip.
Would be nice to know what she published in that time frame. But given Miller's beat and his proximity to Plame, may I suggest Alan Foley?
Since she wrote about WMD's for a long time, maybe she already knew about Plame, and blabbed after Wilson's article.