Well in this case, I'm calling the rule stupid on the grounds of logic. What logical reason does she have to not allow sex in her house?
And I know cars aren't exactly uncommon places for sex, but if someone would rather have it in the comfort of their room, why not?
Janey: I look forward to seeing your reply once you've recovered from shock.
I believe in the principle of compromise, no matter the situation. It's fine that in some situations a person will absolutely and unequivocally say "no, it's my way and that's final" when they have a right do so (such at in one's own home), but I think that even parents should try to compromise sometimes and see things from the point of view of their children as well.