Sue,
Unfortunately VIA doesn't really have an equivalent to Amtrak's Roomette. They have a Cabin for 2, quite similar to Amtrak's Bedrooms. But the VIA Cabin for 1 is a room that only holds one person, so you'd need two rooms and your daughter would be on her own at night. Normally, the price is the same for either of these choices; meaning, you'll pay the same to get a Cabin for 2 as you would to get two Cabin's for 1.
The cheapest alternative would be two Berths. This is setup kind of like an Amtrak Roomette, in that you have facing seats & the seats slide down to create 1 bed and another drops down from above. However, unlike an Amtrak roomette, there is no wall & door separating you from the corridor. At night when the beds are down, heavy curtains enclose the two beds to shut out the light and provide some privacy. But during the day, when the seats are setup, you have nothing separating you from people walking by.
