My 15 year old daughter and I are planning on flying into Rome, staying 8 days, then 3 days in Venice. From there we are going to catch the Bernina Express line from Italy to Chur where it lets off. Originally the plan was to go to Paris but she really wants to see Switzerland for 4 days or so. We aren't interests in cities, but want to see the beautiful countryside, and possibly the Apls. I'm not familiar with the country at all, and know nothing about the train routes. What would be suggestions that we could see or go to before heading onto Paris? Would we need to come back to Chur to connect with the Paris train? Thanks for any help!
The Bernina Express (or more correctly the Bernina railway, on which many trains run) goes from Tirano in Italy, over the Bernina Pass to the Engadin valley (St Moritz etc.), then on to Chur.
From Venice, it is already many hours to get to Tirano, via Milan. From Chur, if you want to go to Paris, you get a train to Zürich, and then a connecting TGV High Speed train to Paris.
You don't have to "come back to Chur to connect with the Paris train", wherever you spend your 3-4 days in Switzerland, you can go from there direct to Paris, changing wherever is convenient.
If you want to look at a map, there is one here: https://www.sbb.ch/content/dam/sbb/de/pdf/freizeit-ferien/ferien-kurztrips-schweiz/internationale-gaeste/sts-geltungsbereich_en.pdf
All the red lines are rail lines, and they all have at least one train per hour, so you have plenty of choice.
I suggest you stay somewhere along the Bernina line, you don't have to do the whole route in one go. Tirano and Chur are in the bottom right corner of the map. Pick any of the names along the route, and look them up. I like Poschiavo. Or you could choose Arosa (South-east of Chur), or man others.