Haha. If figuring out which room of the house was most appropriate for a life sized piece of early 20th century cardboard cheesecake was easy, I would have bought her myself.
If it helps with your ongoing guesses, no I don't live in Hollywood: I live in the middle of farm belt Midwest USA, and I found Marilyn inside of an actual barn.
Your guess is as good as mine why anyone would have a need for a historically accurate butterbox. BUT you have a point that it could be useful for staging historically accurate shots at a film studio. Now I'm going to be eyeballing everyone at the flea market trying to determine whether they are film studio employees or just crazy.