What kind of car do you have? You might be able to run something around the seat or headrest and attach it there. If she's having trouble sitting or laying down, you might want to extend the tie-down a bit longer. I'm glad it's working (sort of) well for you, though! Middie had the same issues with the previous harness setup and I just made the leash a little bit longer so he could turn around in circles. If he can't do that, he forgets how to sit or lay down.