Looking at residences, it looks like the following:
Thomas MacKenzie, Fenton as Agricultural laborer
Alexander MacKenzie, Armarnock in Argyll 1848 Gardener
1851Bonnigton Bank, St. Cutberts, Gardener
1861 Coulmony House, Nairnshire (House sold in 1775 to Ann Brodie of Lethen, Property of J. Brodie Esq) Gardener
1871 Mansion House, Turin Estate, Aberlemno, Angus
Thomas MacKenzie (Alexander's son)
1871 Monzievaird and Strowan, Perthshire, Gardener
1881 Ballechin Garden Cottage, Logierait, Perthshire, Gardener
1910 Appletreeleaves, Langshaw, Roxburgh, Selkirk, Gardener
William Hay MacKenzie (Thomas' son)
1901 Colen Den, Scone, Perthshire, Assistant Forrester (property of Earl of Mansfield)
1907 Dean Castle, Kilmarnock, Ayrshire (I have the offer letter)
Based on the above, the only later interaction with the Brodie's would be around 1861 when Alexander MacKenzie worked at Coulmony House. That seems to be the only dates that fit and probably recent enough for my great grandmother to remember. Perhaps she was relaying what she had been told.