She might be sitting near the back of the room, near the edges. Not all the way back, because that would increase the likelihood of being called upon. She appears indifferent to her surroundings, possibly indulged in a new book or theory (or most likely having a long-winded argument against herself).
Her calm demeanor and simple attire draws no attention to herself and others would easily pass her by. In modern lingo, she perfects the art of ‘winging it’, through caffeine boosts, last-minute inspiration, and under desperate measures: dumb luck.