Thanks for your reply Darryl
IF I have the right person Mary Ann McKenzie was born in 1841,  all the records I can find give Fodderty as her birthplace, but I can't find a record of the birth, maybe her mother returned home for it.
The 1851 census lists: (all born Fodderty)
Alexander Mckenzie  abt 1816 Head 
Ann  "                        abt 1812 Wife
Alexander "               abt 1840 Son
Mary "                       abt 1841 Daughter
Colin "                       abt 1845 Son
Donald "                    abt 1846 Son
Margaret "                abt 1848 Daughter
She first marries on 11th June 1859 to Donald Grant
She was a domestic servant and he a farm grieve both at Feregorm (or Foregorm) of Ferrintosh - I can find Ferrintosh but not the actual farm or estate.  Both the marriage certificate and the 1861 census give a birth date of 1839.  By the time of her marriage her father had remarried, so, I don't have the maiden name of her mother.
Their daughter, Isabella, was born in 1860 and I have no other information about her.  Donald died in 1863.
On 8th February 1870 she married William Rayner of Waterbeach Cambridgeshire.  They had 3 children (John 1872 - my grandfather, Elizabeth Beatrice 1877 and Mary Ann 1880).  She died 26th November 1884.
Hope this is of interest, it would be good to know if this is 'your' Alexander.
David