I found myself agreeing with many posts here, some with conflicting viewpoints so I'm not so sure but the extremely subjective notion I get is that she is starting to get scared she's not gonna get out of this and the impression of her character is that she's the sort of person who fakes something to get out of things, even if just for one more day. IMO some of her hand movements were reminders of duct tape. And because her natural response when in trouble is to lie, lie, lie, it's gotta be killing her to be sitting there quietly and not able to respond to the accusation by inventing lies, except through her attorneys. Maybe some real nausea thrown in by the reminders of the body but she was rather unconcerned about all the talk about the decomp smell. (But maybe it's because she never smelled any decomposition, it was just squirrels and garbage in her car.)
I don't believe it was a ploy by the defense team, at least not all of them, because I think the female attorney tasked with patting her back would have attempted to look a little bit more concerned if they were wanting to convince the jury that she was sick.
In the end, after a day when everybody cared only about Caylee, she had to make it about her.