http://stlouisreview.com/article/2014-11-06/obituary-sr-margaret
Sister Margaret was Principal at St. Dominic High School, from 1974-78, when I was a student there.
The Dominican Sisters lived in a building near the high school, in O'Fallon, Mo. She was there from 1962-1979, according to this obituary, and was the Principal from 1968-1979.