Amy, this is the only Christian Mackenzie born in Tain, in the period, in the whole of R and C from 1760-1770 and matches the date above.
MCKENZIE,CHRISTIAN,DONALD MC KENZIE, CHRISTIAN ROSS OR MC FINLAYMORE,U,24/05/1769,082/10 62,Tain
so for their children we have Janet born 1787, Christian born 1788, Ann born 1790, William born 1792, Anne born 1797, Hugh born 1801.
Isobel b 1806, Neil born 1807, William b 1809, William b 1810.
so this would fit her birth if she had the last one at 41.
"Church of Scotland: Old Parish Registers" database, National Records of Scotland, ScotlandsPeople (https://www.scotlandspeople.gov.uk: accessed 07 May 2019), William Ross and Christian McKenzie, 15 April 1786, Urquhart and Logie Wester; citing Parish Number 084, Reference Number: 20 73.
"Scotland Births and Baptisms, 1564-1950," database, FamilySearch (https://familysearch.org/pal:/MM9.1.1/X1D3-3BP : 10 February 2018), Christian Mac Kenzie in entry for Janet Ross, 03 May 1787; citing , reference , index based upon data collected by the Genealogical Society of Utah, Salt Lake City; FHL microfilm 990,585.