The fact that a reporter is going jail makes me positive that it is not Rove. He would never allow that to happen, he is the ultimate opposite of Clinton and Co.
Miller's source is obviously not Rove. She knows that Rove was Cooper's source, and that Rove gave him permission to disclose the notes. If she's going to jail to protect Rove's identity, then she is a bigger fool than I thought... And that is a pretty big fool!