My .02: If she'd want the MT only for fuel economy reasons, and almost all the driving will be on the freeway at steady speed, I'd have to say get the AT for her and let her be happy. Fuel economy will make little difference on the freeway at steady speeds, and the AT may even do a bit better. (For details see consumer reports review 12/06 which gave city/highway/combined miles for the MT and AT. From memory, the MT won overall, and did much better in city milage, but slightly worse in freeway mileage than the AT - sorry, can't recall the exact #'s off the top of my head)
IMHO the MT is much more fun to drive. But if your wife was 'spoiled' by a Camry, I'm guessing the 'fun to drive' factor isn't a big deal for her
This is coming from a die hard MT guy. The Fit's AT actually pretty good as slushboxes go and for all freeway driving, mileage is pretty much a wash. Get what makes her happy....