Rome to Milan - Itinerary suggestions for a 15 day trip with my daughter

Lake Como is beautiful. Stay in Bellagio and explore the lake by ferry.

A 2 night stay is only 1 full day in a location
Both Rome and Florence need more time

You can day trip to Siena from Florence

I would pick either CT or Lake Como but not both
Your choice may be determined by what lodging is still available. Both are very popular and will be extremely crowded

I’m counting 15 nights-not 3 weeks

Personally, I would cut out the Cinque Terre and spend more time in Florence. We were in the CT last year in early October and the crowds were horrible. I hate to think what it’s like in June. And I would opt for a couple of days in Lake Como, a close train ride from Milan and a lovely place. We love Varenna.

Milan is worth a night or 2 itself.
If you have any interest in The Last Supper you will need to see if tickets are still available for your dates.
https://cenacolovinciano.org/en/

The Duomo and rooftop terraces are amazing.
https://www.duomomilano.it/en/

The Monumental Cemetery is super interesting.

Another option rather than Como is Lago Maggiore. Stresa is lovely and probably not as crowded as anywhere on Lake Como, better chance of finding availability as well.
You can stay in Stresa the night before your flight as there is a direct to airport bus from there- closer than Milan.
https://www.safduemila.com/linee/alibus-malpensa-lago-maggiore/
(Scroll down for English)

If you go to Lake Como you will probably have to return to Milan or stay at the airport night before your departure

Thank you all. I think we’ll adjust to add a day in each of Rome and Florence, with a possible day trip to Siena. My daughter is set on Cinque Terre so we’ll keep our 2 nights there.
We will explore Milan together for two days before we leave, and with my three solo days I’ll explore como and area, perhaps stay a night or two in Lake Maggiore/stresa. Any other suggestions more than welcome as we close in on our final itinerary. Thank you again.

A 2 night stay is only 1 full day in a location
Both Rome and Florence need more time

Apologies to this poster, but they've managed to make two comments both of which grind my gears.

First, two nights guarantees a minimum of one full day in a destination, plus at least parts of two additional days. There's nothing about staying overnight that erases time from one's life.

Second, no city "needs" a set amount of time. Sometimes a soupçon is all one has available; it can be a delight nonetheless.

Bottom line: these folks have essentially two weeks in Italy. I personally would not devote the time to the Cinque Terre villages they're planning, but I'm not they. I will also say that six days in Milan would be a surfeit for me, personally. Bologna is a short train ride away, and well worth a day trip at the very least.

Apologies to this poster, but they've managed to make two comments both of which grind my gears.

First, two nights guarantees a minimum of one full day in a
destination, plus at least parts of two additional days.

Apologies to this poster but "A 2 night stay is only 1 full day"
Of course there is the half or less day before and after that 1 full day.

I did not say that a city cannot be enjoyed with less time.
Sorry for grinding your gears.

I like your revised plan. My only thought is whether you might want to go somewhere more lowkey than Lake Como to decompress a bit after your time in Rome, Florence, and CT with heavy crowds. A smaller spot with a slower pace might be nice before meeting back up in Milan? But Lake Como IS beautiful, so it’s a tough call.

thanks @catmom. I agree with the relaxation goal after the busy travel before Milan. I have three days (2 nights) before meeting up with my daughter again. We'll spend a day (or a day and a half, to be precise) in Milan before heading back on the 16th. So I would like that relaxing time or activity somewhere within hitting distance of Milan, but I don't know what that is yet or if I should leave Milan to do it. Is there some relaxing day trips I can do from Milan? Should I leave Milan and travel solo for a couple of days to a more relaxing (less people) location? That's what I'm researching now.

While daughter works: I would pop over to Turin and enjoy that city before heading back to Milan.
I just don't think the lakes would be as fun solo.
Milan has its fans, but the main sites can be seen very quickly.