The
hot springs in banff are pretty good, especially during the winter. (There's actually better hot springs deeper into the mountains, but if you plan to just do a short trip, Banff is on your way to LL).
Snowshoeing is a good time, if your girl wants to get out and get some of that winter experience without skiing/snowboarding. As well, you can also do sled-dog tour rentals in Canmore (between Calgary/Banff). I've never done it, but I've heard it's a great time.
The Banff townsite is really touristy, which may or may not be your thing. Cave & Basin national historic site (where Canada's first national park was founded) is a nice site to visit if you're going to the hot springs in Banff, but not necessarily worth going out of your way for.