I'd suggest tapping into the actresses that are in each of us. As in: turn it into a game.
Talk with her about the rules ahead of time, and get her on board. And YES, filming would be a fantastic addition to the game so that you can score them for "points" as well as for laughs! (Remember, keep the whole thing FUN). Purely in American Manners there are several different recognized styles... but you can branch out to really have a ball.
For ex)
1 night: Dining like a princess. ((Watch video of state dinners/ etc)) Certain things involved in this "theme" would be tiny bites, perfect posture, and *always* having a smile on your face or interested expression.
Another night: Eating like a trucker. Examples would be elbows on the table, hat on your head, one hand always on your coffee.
Another night: Eating like a restaurant worker (this means you have only 5 minutes to eat, and you have to talk *constantly* while you're eating).
Other examples of "Eating or Dining like _________"
- A diplomat
- A movie star
- A grandmother (with or without teeth)
- The person sitting to your left
- ANY character on TV
There are even "deportment & dining" classes offered through various hotels. For a "cheat" La Femme Nikita has a scene, as does Pretty Woman, as does My Fair Lady. Watching all 3 clips can be pretty interesting.
Point being: We often don't REALLY understand what our "normal" is, until we try to imitate someone ELSE'S normal. If she's at all into spies, you can have her pretend she has to maintain her cover in a certain enviornment. If not, go the actress route. Regardless... once you get her REALLY trying to eat or dine in a myriad # of different ways, it'll be pretty easy to chuck her old way.
I'd also suggest doing "theme" nights yourself. Loll all over the table and giggle at yourself. Sit prim and proper. Eat as fast as you can. Eat as sloooooowly as you can. Pretend to be old and not have any teeth. Rent a full dining set for one night and use all 9 or 16 or x pieces of silverware & glassware. Learn how to "talk" to your waiter by using your silverware & dishes & glasses (like how to hot chocolate by how you place your spoon ... arrgh... can't find a link online with all the cool tricks... but most dining etiquette books have the list).
Personally... having grown up with FAR too many state dinners... I absolutely *revel* in putting my elbows on the table. But merely knowing how to move seamlessly though many kinds of dining is a skill I'm SO glad that I learned.