I was there in late July. It was 98 degrees and crowded and practically nothing had AC. But who cares, it was VENICE! She will love it and could probably spend 6 months there. Have a great trip!

Our first trip to Venice was 4 nights (with 4 full days) and although I wished for more time there, I felt that it was just the right amount of time. And....we never made to any of the islands.

Naturally, my next trip to Venice will be at least a week. My list of "things to do/see" in Venice is still full (and is still growing). We just steered far away from the crowds and got "lost". It was magical.

What a great adventure for your teen!

beeswing--

Given your travel priorities, I'd cut a day from Venice. I love Venice, but it is a city best taken in small doses, especially with the crowds. As you can see from the above comments, three days would let you get an idea of what is there, then you can make a list of what you want to do next time.

I would add an extra day to Florence, as you can barely scratch the surface in three days.

Three days to see Paris proper is enough the first time around. I'd use the extra days to rent a car and drive out to Normandy to explore the beaches and cemeteries, then drive down to Mount St. Michel and stay on or near there. Drive back to Paris the next day, stopping at Chartres.

You can do Pompeii as a fairly easy day trip from Rome, booking with a tour company or renting a car. And you should see Pompeii.

I'm not a big fan of Venice, but I wouldn't cut your time there. I also wouldn't cut time from the cities for a lot of day trips either. Maybe Pisa/Lucca from Florence, maybe Tivoli or Ostia Antica from Rome, maybe Giverny or Versailles from Paris, but probably not all. You'll be moving at a non-stop pace as it is without adding day-trips.

Enjoy this special time with your daughter. You're all going to remember this trip forever.