I think she always looks like that. Seems like a serious, workahoilic type.
About a year ago, at the meeting where POTUS and VPOTUS both put their water bottles on the floor, it looked like FLOTUS and Sec Nielsen were the lookouts. Nielsen was extremely intent and seemed to be staring the entire time on her papers. Really intense. I think it was her who gave the go sign, on a verbal or nudge from FLOTUS, who was sitting kitty corner next to her. The go action sequence started with Perry closing his notebook. FLOTUS Could see the whole table from where she was.