And don't let her think I could or would approve of anything untoward. Part of me thinks it would be sexy, but it would also be reckless, and I don't approve of her taking stupid risks like that with our health and our family. Convey that to her wholeheartedly. Start on that at the next opportunity.
No. Do NOT convey that to her (the bold part). Convey to her that you'd kick her out the door if she ever crossed the line with any guy, and you'd expect the same from her.
If you say what you said above, it'll stick in her mind like a burr. Like the boy whose mother, on one normal Wednesday, jokingly told him "I really wanted a girl, you know" ... and who was never able to forget that, and never felt the same sense of security in his mother's love as before.