You Think They'd Notice....
Towards the end of the movie when Chris and the kids pass the parents on the highway, just as she takes over them at 80mph, the mom says, "Look at that lunatic! Brad and Sara are gonna be driving soon, they're gonna be on the road with people like that" - The parents look directly at Chris's car, surely they've got to notice it's her and the kids Wouldn't they have seen it parked outside their own house when the leave for the Associates Party?
Also, when Chris, Brad and Daryl leave the French restaurant after confronting Mike, there's a billboard poster of the Playboy photo clearly in view, and Chris suddenly looks around and notices Sara isn't there - wouldn't she have seen the Playboy photo? She only sees it for the first time later on at the Frat Party, prior to that, Brad and Daryl have the magazine in the back of the car.
And - when Sarah is hanging outside the window to the Associates party, you would think that out of all those party guests that one of them (if not a few) would see Sara outside the window! But no, nobody seems to bat an eyelid that she's there.