Hey Sylvia,
I may be able to help you a bit, I was trying to find my great great uncle David Stewart born 1853 in Lochlee who seemed to disappear after 1881.
Unfortunately I didn't find him but I did find a death for a David Stewart February 10, 1910 aged 89, parents were William Stewart and Ann Moir. He also left a wife behind Ann Will. Apparently he had broken his leg and didn't survive. The informant was his son-in-law (my gg uncle) James Stewart who had married Isabella, John Dewar Stewarts sister. It may be significant to note that David was living with his daughter Isabella at Waterside Cottage in Lochlee at the time.
According to
http://www.deceasedonline.com , John Dewar Stewart was buried December 10, 1948 in Brechin not sure about Martha but getting John Dewar's grave details may result in burial details for her.
Curious to see if your branch is a twig or part of your main line.
Jeff