Their address on the 1920 Census was 56 Mozart Street, and the 1928 Boston city directory says that Edward Doherty of that address died 4 Mar. 1928. I don't see a Mary listed as a widow of Edward in the 1928 or 1929 city directory, so maybe she was deceased by then. There is a listing in the 1929 city directory for a Mary T. Doherty who died Aug. 1928, but it doesn't give any further info about her. There's at least 20 women named Mary Doherty in that directory, so it may be only coincidence.