The 'Nothing In Life Is Free' attitude has worked WONDERS with our JRT. She too is 16mth old but has always been very sociable, although very ill-bahaved. She genuinely thought she was head of the house.
Now, she does nothing without our permission. I put her food down and make her eat it immediately. If she doesn't, it is removed. ALWAYS ignore her for 5 mins or so when you first enter the room. NEVER play with her when she initiates it. All the nose nudging and toy dropping must not instigate play. Wait till she is resting or busy with something else, THEN invite her to play. She thinks