After finding her in a 1900 census, it turns out "Lawless Mary" was not a nickname; her name was Mary Lawless.
The 1940 census enumerator had just added a line indicating her surname was the same as the name abover her: Cone. But, her name was, in fact, Mary Lawless and there is not an amazing story.
So, if you were researching Mary Lawless, how would you have found her? I think the most likely way would have been to search for her daughter, Susie, in the census.