Try this one on for size: just start escalating with her on the sofa. At some point she'll either be so into it you can just pick her up and carry her to the bed (and toss her on it - tons of fun!), or you can just sleep with her on the couch.
If you have roommates and they're there / you're worried about them coming home, either give them a heads up, or take the girl straight to your room to look at something on your computer / watch a movie on your computer, etc. If she asks why not the living room, just tell her your roommie's coming back soon and he always watches The Shield or some other show that no woman on Earth wants to watch when he gets home.