Prague-Austria-Switzerland-Frankfurt

Remember that with moving around you get one fewer day at a place each time than the number of nights. So 2 nights in Salzburg only gives you one full day there. That's not a lot of time to visit the gardens, the horse fountain, the church, the graveyard, the church bakery, Mozart's birth-house and his living house (across town from each other), the fortress, the museums, the walk on the hilltop, 2 or three of the coffee house bakeries (must do, IMHO), the dancing boat ride, any Sound of Music touring you have in mind, and all the many other things I have left out.

Luzern (local spelling) is an excellent choice, even if your daughter didn't need to go back.

But you have 3 nights there and 4 nights in the Berner Oberland - that could be quite a lot of Alps. Will you have some time on the lake steamers?

Interlaken is a train junction and in the flatlands. I would choose either Lauterbrunnen if you would like to be in the bottom of the valley and have access to either side, or Wengen - up one side - or Muerren (my favourite) higher up on the other side.

Awesome input Nigel.

Great points about "Alps Overload" and reminder that the first night in a town- includes "getting" to town and is not a full day.

Salzburg sounds like it deserves an extra day-

Excellent input on Luzern and flatland Interlaken. Will adjust accordingly.

When you go from Prague to Salzburg stop on your way in Cesky Krumlov. Small town but a gem. Almost all Americans in C.R. see Prague and Cesky Krumlov.