Fact or Fiction? Part I

I've been remiss about posting here, and I wish to apologize to anyone who has sent me news links because I haven't been polite enough to at least thank you. A Garbo incarnate, however, has recently emailed me with a tidbit that I must share here:

Marlene Dietrich hosted a dinner party for Marilyn Monroe, where psychologists invited by Dietrich ambushed Monroe.

This sounds like the best Intervention episode to never air, but did it truly ever happen? Let me know whether you've got evidence to support this tale. At the very least, let me know whether and where you've heard or read about this. In the meantime, I'll conduct my own investigation.