Thank you Wray and Darcy!
Yes, 187peixoto, my brother and I are both vegan and we did the Heart of Italy successfully. We talked with the guide after the first meet-up and she was able to get us vegan options for all group meals. We also always travel with some back up food in case there is an issue. I always have Clif Bars or nuts or some other option. We also asked her to let us know if there was a problem at a particular restaurant and we could forage on our own. No problems at all. For one of the meals on our own in Volterra we found a wonderful vegetarian restaurant but I noticed a few years ago it had sadly closed (pre-Covid).
A few years later we took the Village Italy tour (same guide, lol!!) and there was one time when a restaurant tried for vegan but didn't quite get it. It was the cooking lesson location and they served us a starter with egg in it. They were trying so hard both my brother and I ate some of it to be nice. Sometimes you just have to opt for being a good guest.
Sometimes is a restaurant offers "fresh" pasta it will have egg in it whereas dried pasta often does not so if this is an issue for your travel partner, be sure to ask. I also found that while I am not GF, the GF pasta is dried and it was also eggless so that is something to consider. My back up selections are often Bruschetta (senza formaggio - without cheese) and a soup - Ribollita is often vegan as is their vegetable soup. The best soup I've ever had was Tuscan bean soup in Volterra....my word...wonderful!
The Cinque Terre is a seafood-heavy area but it was very easy to find vegan food in the restaurants there. One of the things I loved was some kind of fried chickpea dough...my word!
I'll add that I've done 11 Rick Steves tours as well as 11 Road Scholar tours to Europe and have almost always been able to get vegan tour group meals as well as meals on my own that have been suitable. On all of those tours there was only one person I ever noticed who was having issues with food. On a Road Scholar tour one of the members was doing a very restrictive diet plan (similar to FODMAP) that had just too many particular things she did not eat. Being vegan was no problem compared to that.
I also carry printed out cards saying "I'm vegan" with explanation (https://veg.ca/2013/01/17/vegetarian-travel-translation-cards/ ) and have downloaded the V-Cards: Vegan Abroad app to my iPhone. I like to be able to hand the server a card to take back to the kitchen if they need to. I've had them come back after a conversation with the chef and point out what will work on the menu. A couple of times I've had servers say "I'm vegan too" and offer to have the chef to fix what they like to eat there. That's ALWAYS been a wonderful outcome!
Have a wonderful time!