Yeah, something closer to 44cm is probably what would fit her. My road bike is a 48cm frame, but for a cross bike I need a 44. I have my eye on a pretty Redline Conquest Pro...*sigh*

Good luck finding a cyclocross bike for your wife. I agree, if a person only has one bike, that's just about perfect. In many ways I regret not going for a 'cross bike first. A ton of the roads to our north are unpaved. I look at them longingly when I am out on my road bike.