The only candidate for Margaret Proctor (nee Forrest) in the 1841 census is this woman Margaret Proctor (born circa 1771), with John Proctor age 35 (a stone cutter) and Elizabeth Proctor age 25 at Old Comely Bank, Edinburgh St Cuthberts. This does not appear to be the woman we are seeking. In that case she has either died before 1841, is not living in Edinburgh if alive, or has remarried