I'm not sure what you mean by "truckle" bed. Are you talking about a trundle bed, or a roll-away bed/cot?
If you mean trundle beds, those are not available at CSR; only at POR in the AB section. They cannot be added because a trundle is part of the bed frame and cannot be moved from place to place. And depending on the size of the teen, I'm not sure she would fit comfortably. Trundle beds are generally meant for children. A small adult might fit, but might have to scrunch up a little.
I don't believe roll-away beds/cots are available at any of the resorts probably because WDW feels it could lead to overcrowding in a room. They're pretty strict about how many people they will allow to stay in a single room.
ETA - also, it would probably be very difficult, if its possible at all, to fit a roll-away/cot in a moderate resort room.