David and Theresa Ludlow of Fredericksburg, Va., announce the engagement of their daughter Margaret Gillan Ludlow to Nathan Thomas Ritchie, son of Patricia Ritchie of Yorktown, Va., and Ryan Ritchie of Champaign, Ill. The bride-elect is the granddaughter of Charlene Norton of Fredericksburg, Va., Ben Bollard of Charleston, S.C., Roberta Luther of Gainesville, Fla., and the late Ed Ludlow. She is a 2008 graduate of Stafford High School in Fredericksburg, Va.