I'm sorry to pile on, but arriving in Venice all tired and jet-lagged and it will be at least noon, probably later if you are hungry for something, anything to eat, before you can see anything of this most beautiful and atmospheric of cities, and then you will tire easily - even if only 23 - (where are you flying in from, Andy, is this after a connection somewhere or a direct flight?) and then in the morning when it is beautiful and you decide you love the place, but then you are off to Verona (lovely place and a great excuse to go there).
It would be such a shame to go away with bad memories of Venice because you only saw the tiniest bit of it when you were tired and rushing. The way to appreciate Venice is to give it the time and space to get under your skin and mesmerise you. That takes more time than you and she are giving it.
I'm probably biased because I go back to Venice every year - after 10 years of at least once a year, often more, I have barely scratched the surface.
If there is a chance what I said, you might just leave it out altogether this trip. It is special.
The other thing is that you are doing all this moving around in July. That's just about peak season, for both numbers of tourists in each of these places, and for temperature.
Unless you and she work outdoors somewhere hot - like Texas - the overwhelming heat may get to you. Certainly in Florence which is in a bowl and is hotter than the surrounding area, and in Rome where the heat just sticks.
The crowds will be unbearable in the Cinque Terre, where it is hard to avoid them, and elsewhere where it is a bit easier. The Amalfi Coast will also be wall to wall. The CT and Amalfi Coast both suffer he they have crowds because they are both on rocky coast so there is very limited area for all the people to share. In Rome, and Venice it is possible to get away a bit from the crowds by going just slightly off the beaten path, especially in Venice because the attraction is the city itself, not necessarily the paid attractions, and in both Venice and Rome there are plenty of nice cool churches to cool off in, and get top notch art as a bonus, hanging where it was painted to hang or standing where it was carved to stand. That is an experience completely different to visiting a museum.
Verona will be hot too, although I never found that it troubled me there as much as in some other Italian cities like Florence and Rome.
I think it is fabulous that you are doing this trip together. That's wonderful.
Even if you don't get back for several years, you will have planted the seed of Italy in her consiousness and I am sure she will return as often as she can.