When DS1 was in 7th grade, I went with him (and 50 other kids/parents from his middle school) to Europe through EF Tours. It sounds similar - we flew over and then took either a tour bus or train place to place. Lots of hotel changes, most for one night and little down time. Sink washing would not have been doable so I would pack accordingly. Of course this was pre-Covid but everyone on the tour seemed to check a medium-sized roller/spinner bag and carry a backpack carryon. Backpacks doubled as a daypack. We did lug our bags up stairs, through train stations and down streets but it wasn't bad. The kids never complained, especially since everyone was doing it.
Our family generally travels carryon only. My kids all have the smallest Monos carryon. It's a great little spinner bag and has put up with lots of abuse - dragged through airports, train stations and cobbled city streets. We can definitely fit 10 days worth of clothing but that's with careful rolling and organization. I'm not sure my high school boys are neat enough to maintain it alone. They make larger bags and if I were in the market for one, I'd definitely consider it. It seems to hold more than expected while being easy to handle. Packing cubes always sound good but I've never been able to fit as many clothes when using them. For a carryon, they use their regular backpacks. We bought Cotopaxi Allpa travel packs for a trip this coming summer with luggage requirements. I really like how those open like a suitcase and have some organization. DS1 used his this past summer when we went to Italy. He seemed to like it but he was always carrying a backpack on his front and back on trains and through airports since we didn't check our bags. He wasn't bothered but others may do better with a roller or spinner.
Hope your DD has a wonderful trip! She will make such great memories!