I'm sorry, but I've had to remove your ancestor as a daughter of that particular Charles MacKenzie of Letterewe as the dates you've given would make this woman an older contemporary of Charles's, and not his daughter. The following information is in the "History of Clan Mackenzie," pages 357/358.
"The Mackenzies of Letterewe
Kenneth Mackenzie, VI of Gairloch, married, as his third wife, in 1658, Janet, daughter of John Cuthbert of Castlehill, Inverness, and by her had issue -
I. Charles Mackenzie of Mellen (sic) Charles, and I. of Letterewe... He married Anne, daugther of John Mackenzie, II. of Applecross (sasine 1687), by whom he had issue..."
Given that Charles's father married his mother in 1658 (unless there are very obvious reasons to disbelieve what we have in the Mackenzie history), Charles can't have been born earlier than 1659.