Is there much time between teatime and bedtime? Does she still have a day sleep? I wonder if it's because she's tired. Is she expected to stay at the table until everyone has finished dinner? What about other meals? (Sorry 20 qu's LOL)
I don't really like getting into food fights, there are still some foods that I won't eat because I developed such a bad 'taste' of them after being force fed (to some degree) by my parents when I was young.

With my girls I say if they've had enough, they can get down. I'm just going through a phase at the moment where they have been changing their minds

so I need to put the plate up on the bench when they say they've had enough. Just an idea with Miss Lucy?