Oh also, this may have already been said but it's so importaint...
Ask about her hospital transfer rate. One midwife I interviewed seemed to be overly transfer happy according to some of the stuff she was telling me about monitoring, so I asked her about her hospital transfer rate and she said it was about 50% for first time moms!?!?@>@!>!>!! Needless to say I didn't use her, but I know of someone who did and ended up being a hospital transfer.
Another thing I just thought of that mayb be helpful, ask her to describe what her tipical "role" is durring labor. My midwifes ended up being very hands off and "just do whatever feels right" kind of ladies, which was great to some extent, but I was pushing for over two hours in one position and feeling very unsucsessfull, as a first time mom I would have liked the midwife to take the initiative to suggest some other positions, stuff like that is oh so importaint when choosing a midwife. OH and I'd also suggest interviewing AT least two if not 3, just so you get an impression of different styles.