Where does SHE want to go? I have done similar trips with my daughters and usually they have a slight idea of one place, and then we build from there. I like the idea someone had of Paris, Amsterdam, and Bruges/Ghent. London would be good too, but for me, staying in one place 7 days feels like too much (shrug. I just feel ready for somewhere new after about 4 full days). You can always return. I also find that being in major cities can start to feel oppressive. Maybe weird, but I like to go big city, smaller city or town, big city, etc. The town/smaller city gives me a sense of catching my breath, and then Im ready to tackle a big city again. Thats why I like the idea of Paris, Bruges/Ghent, Amsterdam. I also like this idea because AMS is one of our favorite cities (mine and my three teens). Its lively, charming, energetic, and the size is such that you can get oriented fairly easily and start to feel like you know your way around. I avoid the center of town (red light district area) bc we find it the least interesting. So when you read reviews about crowding and partying, they are usually describing that area (although yes, the city is crowded). The other reason we love it is that we always rent bikes, and if you are comfortable with this, biking around AMS opens up the city in a whole new way. It gives you quick and spontaneous access to the entire city (because biking from one end to another takes 15-20 minutes), and it puts you in close contact with the streets and directions and locations of things. Plus, biking is just fun! On one visit, my 13yo daughter and I biked out along the Amstel river simply by following the water (no map. The idea came from RS' book though). Within minutes you are seeing cows, windmills, and rowers out on the water. A nice breather from the city and good perspective of the countryside.
Anyway, that was a longer spiel than I intended. In short, ask your daughter where she wants to go ;p