Miller MUST HAVE known a lot about Wilson from being in Iraq and having a "special" security clearance. She probably knew Valerie also because of their mutual interest. I believe Miller had special clearance at the CIA also.
Searching Amazon, you find Plame the Flame's book, "Germ" Although a lot of the info supplied to her was from Chalabi, I'd wager that she got a lot of stuff from her contacts in the CIA WMD division. Namely, PLAME. I'm sure they've known each other for years. That's why Miller wanted her questions and testimony to be very limited. I was really surprised when Fitz agreed.