In the Cavalier book I got, they suggested getting a small section of sod (grass) to put in the house, and keep it by the door, and have them go on that, so it's like going outside, it's near the door, then it's only one additional step to get them to go to the door when they want out. I like the Pheramone idea, too...maybe do both? If you can't stick a stake in the grass outside (since it probably isn't yours to "decorate"), then maybe you could just spray the grass right before she goes?
Good luck! It sounds like a tricky situation!
Jenni, Scott, Corgan (blenheim), Celti (Corgi-mix), and Luna (kitty)