This "lady's left elbow on the man's right elbow" is all very well in theory, but in practice, it may be impossible if the couple's heights are similar.
Try this test. Bring your right arm across so that the right elbow is on your left elbow. See where your right hand ends up?
THe distance from my fingertips to my elbow is 17 inches. But from elbow to shoulder (even the top of the shoulder - further up than the lady's hand should be) is only 12.5".
Would it maybe be more accurate to say the lady's forearm should rest lightly on the man's upper arm?