Mary Graham of Leitrim near Castledawson

Hi there

I have completed my research on our family tree for the Graham and Leslie families, but am missing a vital date; the death of my grandmother,

My grandparents married 22 April 1902 at the Castledawson Presbyterian Church. My grandfather was George Graham and he died 25 January 1956 • Leitrim, Castledawson, County Londonderry, Northern Ireland (date confirmed by copy of Will and funeral notice). 

I wonder if anyone could find out when my Grandmother, Mary Graham (née Leslie) died? I believe she was alive when my father emigrated to New Zealand in October 1949, but died before my grandfather (he died in 1956). 
I believe she would have died in the Magherafelt District (but not sure of this) and the informant was likely George (husband) or Robert Graham (son) or his wife, Ena. She was born 21 March 1876 at the farm at Leitrim and her parents were Archibald Leslie and Catherine Cahoon.

I would be delighted to know the date she died and the cause of death.

I was told George died of pneumonia, but it would be good to know his cause of death also.

Thank you - Ann