That would be Olga Alexandrovna.She was mature, The Dowager Empress' daughter, and relatively free to travel. Olga N. was just nineteen, studying for nursing, had never traveled outside Russia without her family(even including her grandmother Minnie), and her absence (or this trip) has never been mentioned in any IF writing, diaries or letters.
But interesting newspaper item, I must say.A little "war tourism"?