Out of curiosity I took another look. It could be that Jacqueline is a little more animated than Jill when just sitting there. Jill seems to just pose between scenes where she has lines, there in the courtroom Claire Kincaid (who ever was playing her at the moment) had some small reactions to the dialogue I think. Or maybe I’m grasping at straws, I’ve seen that episode plenty of times, never would have picked up that someone else was there, and they are identical twins.