Italian trip over Christmas vaca

Just to make sure, although you likely already know this, you’ll need to bring the written consent of both her parents to travel with her internationally, ideally notarized and including authorization to make medical decisions in case of emergency.

Personally think it is too ambitious. You really have not allowed for travel days. You lose at least a half day if not more when changing locations. That could be maybe three days with your plan. You id 12 days in location and assuming a arrival and departure day, gets you to 14 days. In my opinion. -- too much. And you lose Christmas day and most of Christmas eve.

I would consider skipping Venice since it will be cold, damp, and somewhat dreary at that time. I would fly into Milan and come home from Rome. You could do three days, including arrival, in Milan, Is there a reason for Medisimo? I am not familiar with Medisimo so am reluctant to have an opinion as to a visit. You need to carefully plan for Christmas day as little will be open. A few restaurants may be open but don't plan on it.

Will wait to see your response before offering more suggestions.

I would take a much closer look at your itinerary with particular attention to your travel days and how long each connection will take (door to door) and by which route. Especially around a stay in Madesimo (note the correct spelling) . It does not have a train station and getting there and onwards will involve a combination of trains and buses. Going from there will take anywhere from 6-7+ hours to Florence or Venice. Essentially a whole day. Spending only one day in Venice (given the amount of time it takes to get there) seems a waste of time. And remember how very short the daylight hours will be. Note closures or reduced hours from Christmas Eve through St Stephen's day.

We have, what I hope are, the needed documents.
Granddaughter asked for some snow days and looking around at the various choices, the Madesimo slopes say they open in November and the Christmas season is crowded everywhere so we’re hoping she can have some ski/toboggan for a few days before the crowds. We are assuming some snow and no crowds, and it is not far from Milan. Also, we have tried to fit in travel days. For instance, about three hours from Milan to Madesimo, then 2 full days in Madesimo, and about 5 hours from Madesimo to Venice, then one full day in Venice, then about three hours to Florence, after which 3 full days in Florence. Then about 4 hours to Rome on Dec 26, after which 5 full days in Rome. So the days listed in original do not include the travel days. Of course, the best laid plans of mice and men …
We’ve thought about eliminating Venice, and I know one should plan with returning in mind, but we also are thinking this could be the unique opportunity.
Thank you for your comments!

There's a Santa Claus regatta in Venice, most likely on Sunday December 20. If I understood your itinerary, you'll only be there on the 19th, but if that's something you think your granddaughter would like, maybe it's worth adjusting your plans a bit?

This sounds ambitious, but I haven't looked closely like you have at the trains.

Florence, after which 3 full days in Florence. Then about 4 hours to
Rome on Dec 26

Christmas Eve expect quite a bit to close early, not sure what are your plans but I would book ahead or plan dinner that day, and what to do on Dec 25th as well. So if you wanted to see anything that requires pre-booking, like the Academia, book ahead. Frankly Dec 24th might actually be a tiny bit quieter, with Italians perhaps focused on getting ready for the evening, who knows? Just so you're aware, Dec 26th is also a national holiday in Italy, but in central Rome we found lots open, especially restaurants filled with Italians enjoying a day off. I would happily skip Milan as you don't have enough time to enjoy much there, give yourself a bit more breathing room. Hope you have a great trip!!

Thank you all for your ideas. The Venetian regatta is appealing, we’ll have to think through that carefully. And Sandancisco made me realize that my “3 full days” in Florence is a bit exaggerated. We’ll enjoy walking and wandering but there is really just two days when museums will be open. Per internet search, it appears that the hours for at least some of the sites should be enough on Dec 24. It will be the meals that we’ll have to plan for. There seems to be some restaurants offering fixed menus. And I hate to not use Dec 26 as a travel day (or the 25th) because things are more generally closed those days. But December 25 is likely to be wholly memorable if we stay in Florence. There is still much to look into as we plan, especially the timing of planes and trains as everyone has suggested. Thank you again.

There seems to be some restaurants offering fixed menus. And I hate to
not use Dec 26 as a travel day (or the 25th) because things are more
generally closed those days. But December 25 is likely to be wholly
memorable if we stay in Florence.

I agree, stay and enjoy Florence on December 25th, especially in fine weather there are some parks across the river, walk up to Piazza Michalangelo & I don't recall the name but a church further up in those hills with fine views of Florence. And there's always church services! I dislike those Christmas & NYE set menus, tend to be pricey and too much food. Might sound weird, but we usually go to a pizza by the slice place on NYE, easy to find something open & no need to eat a large meal!