Thanks largely to the quality advice recieved here, we've settled on a course of action:

1) Go try out as many different bikes as possible at the LBS
2) Watch ebay and the Terry forums for a used Classic or Madeleine (or, failing that, a Symmetry/Isis)
2a) If the auction Catriona posted doesn't go too high, we'll just grab that as a starting point!
3) If we can't get a used Terry in the right size and for a good price by January, then we'll probably pick up a Trek 7.5FX WSD or a Felt ZW30
4) Ride, ride, ride... until she starts talking about her 'next bike!'

Thanks again for the help!