Sister Catherine Ryan, a Franciscan nun and veteran juvenile justice lawyer, was named head of Maryville Academy on Monday. The 5 foot, 2 inch Ryan had to stand on a wooden box to reach the microphones at Maryville’s Des Plaines campus Monday as she was introduced to the media. She couldn’t appear any more different from Maryville’s last chief, the Rev. John P. Smyth, a powerfully built, sometimes combative man who had held the job since the John F. Kennedy administration and was revered by juvenile wards and Chicago power brokers alike.