I'm suggesting there could be a difference between her professional demeanor and her private beliefs. For example, I'm rather wobbly on abortion compared to the average Freeper, but if I were asked for my opinion on whether a pro-choice guy could be a good choice for the Republican presidential nominee I'd say "Hell no, that would just be inviting desertion from the base. It's not even worth considering." And if asked to interview him or anybody during a primary I'd be fairly aggressive on that issue. But personally? I'm not sure I'd care.
I don't doubt that Miers does her job as White House Counsel well, but if Bush believes that reflects how she'll rule as an independent justice I'm very skeptical. I'm also concerned by signs of sycophancy about her, such as the David Frum story that she claims George Bush is the most brilliant man she's ever met. I doubt she actually believes that, but it may show she tries a little too hard to tell the President the stuff he'd like to hear. I'm sure when he says he thinks she'll be a conservative judge he is telling the truth --- but is Miers?
I don't think a nominee's personal beliefs matter at all. What matters is what the constitution says. What is important is that any nominee understands that. Beliefs change, character does not, so character is very important. If you believe that the constitution says what it says then that's exactly what we want on the court. All other issues follow that reasoning.