Why feel troubled? She was responding to her attorney. Maybe he was trying to make her feel more at ease. Maybe they just have a good repoire.
Of course her affect is different when the jury is present. Like every other defendant, she knows the jury may well be watching her. If she smiles they may think her callous, so maybe capable of what's she being charged with. If she cries or seems overly emotional they may think she's faking it, so maybe capable of doing what's she's charged with. Neutral face is best.
She's somewhat exceptional, actually, in that she seems never to have pretended indifference by play- writing or shuffling papers during any testimony. IMO she's presented as attentive and respectful.