Italy is my favorite foreign country filled with history, amazing art and scenic places.
The places you listed are great, but you left out two of my favorite places, Florence and Rome.
Venice is a must, it is special, no other city quite like it and three days is enough do see there.
The Amalfi Coast is great but not close to your other sites. Most people that visit the Naples area also visit Sorrento, Capri and Pompeii. You would need 4 days minimum there to do all that. Also, the Amalfi Coast is in some ways like Cinque Terre, a scenic place alongside the sea. Perhaps you should eliminate either Cinque Terre or the Amalfi Coast FOR THIS TRIP.
Your fiancé has been to Italy and loves those place, I get it, but does she wish to explore new places.
Rome is amazing and filled with ancient Roman history as well as the incomparable St. Peter's Basilica and Sistine Chapel.
Consider a few days in Rome. Florence is another special place, especially if you love art.
Perhaps you should do some research on things to do on TripAdvisor for places in Italy and find out WHAT are the key sites. Then, make sure you and your fiancé agree.