"When I and the people I knew graduated, some of us stayed in academia, most left academia, but when you think about who stayed... notice it wasn't the smartest ones. Maybe physics is different, but the rest of post-doc academia isn't our intellectual cream. I guess if it's the only environment you've known then that might be hard to grasp."

That won't persuade, at all, but perhaps switching her to the condescended-to role will be cathartic.

I'd only say the above if it was actually true for you, and that wording may be a little misleading - in my experience the ones who stayed were a mixed bag and some were indeed very smart, but emphasis on mixed rather than cream, in school I thought academia was supposed to be the cream but I can't shake the feeling that many stayed because they were a bit too useless to leave the nursery, or just not ready. Other prestigious institutions were picking off actual cream (e.g. the local NSA equivalent)

Other people's advice is better, don't do what I said, but I am curious of other people's experiences of the kind of people in their peer group who stayed vs left academia. I was not at a prestigious university.