RE: OTHER EXCURSIONS...It's true that even a week could be insufficient time spent in this relatively small city, but you'll definitely get to hit the major spots at a relaxing pace.

I think that Slovenia and Croatia are a bit far for how much time you have, plus late Winter would not make travel any easier. A Croatian-American friend here in San Francisco recently raved about Ljubljana and the rest of Slovenia as being clean as Switzerland and Austria, as friendly as Italy, at rock-bottom prices. I would make that a separate trip.

Having said that, it would be pretty easy to take a day trip up to another part of the Veneto. Bolzano and surrouding towns at the base of the Dolomites are supposed to be gorgeous, but again the weather will dictate how viable this choice is.

Padua (Padova) is famed for its churchs and mosaics, and it's only 20 minutes by train. From what I have heard and read, I think that Verona is probably not as appealing, but have not been there.

Since Venice is the main focus, perhaps you can choose two or three day-trip options, and surprise her at dinner the night before with something like "Tomorrow we can go to any of these places...your choice!" and you already have the basic plan ready to go...