There are a couple of Mackie stones, but not unfortunately the one you are looking for, however it is possible that your Mary Mackie could be buried in Johnshaven cemetery. Burials stopped around 1891 in Benholm, not sure when they started in Johnshaven.
Inscriptions:
Erected by John Mackie, in memory of his wife Mary Dye who died at Johnshaven 19 Jan 1901 aged 60yrs, His sons William Mackie d 13.10.1893 aged 26, Robert Dye Mackie d in Montrose Infirmary 11.11.1893 aged 35yrs, also his son-in-law William Beattie d 21.02.1908 aged 26 yrs, the above John Mackie d 02.12.1913 aged 79 yrs, Their son George d 31.05.1927 aged 53 yrs.
The other stone is marked on the plan as D Mackie and is very damaged, hardly any inscription remains, there is the name John mentioned and also a date of 1775 and a reference to mother and possibly daughter.
Sorry not to have been much help.
Jean