1901 census lists “Nellie” as Margaret born apr.3/1876
I found the date of death for Eric Clark, Nellie Lawson's second husband. It is May 21,1988.  I found it in the obituary finder at the Collingwood Public Library web site. I typed in Clark and went down the list till I found him and Margaret E Lawson who is listed as Margaret Clark in the data base.  The date of death for Margaret E. Lawson Rourk Clark is listed as 00/00/1961.  The reference for the obituary is EB 17/8/1961.  I am taking that to mean August 17, 1961?
 
The death notice for Margaret E Lawson  is listed as Margaret Ellen Lawson Rourke.
still widowed in 1921 census