Acknowledging good behavior

We all know that we should be acknowledging good behavior right? As a reinforcer. I do that all the time when D shares her toys or if she says thank you and please.
But last night, D pointed out quite a few times that she was sitting nicely in her chair and not moving around.
See for the past few days, she had been acting so antsy and not wanting to sit in her chair and eat a proper breakfast/lunch/dinner whatever. She would move about, chew her food slowly. Aaargh! Basically, annoying me.
One morning I was really mad that she would not finish her breakfast. Later in the day, I got to thinking and really tried to re-adjust my attitude! Who cares if she doesn't finish her breakfast, maybe she wasn't hungry.
So my new tactic is to not force her to eat but make it a point to just say, "Are you full? You are done with dinner?" And if she nods, then fine. She's done. "You may leave the table." I was thinking that maybe she doesn't quite understand how to convey the fact that she just may be full and does not want to eat.
But interestingly enough, last night she was really being a good girl and sat and ate her dinner without jumping on and off her chair and she made it a point to tell me, "Am I sitting in my chair and not moving, mama?"
And I replied, "Yes!! You are! You are being so good!!!"
I think I read somewhere that we aren't supposed to relegate kids to good girl, bad girl references. Punish the deed, not the person? Or something? But obviously that part didn't stick with me because I can't, for the life of me, recall how you are supposed to reference good/bad deeds without saying, "Good girl or bad girl"....must be because I am a dog person at heart.