"Wow, that's a cynical enough view of marriage for 10 people!"
Or, more rudely....no, I wont go there, it's just too trite, and really not nice.
I would have laughed as if she said something ridiculous "You cant possibly believe that?!" "[her answer here]" "oh...{wide eyed expression that makes it clear you think she's crazy}well, then, on to more pleasant topics! [insert topic change here]"