According to "The history of the family of Dallas" author, Lachlan Mackintosh's second wife was Christian, widow of Alexander Dallas of Cantray who died in 1693:
"The latest notice of the laird which has been met with is 4th March 1736, when he was one of the witnesses of the baptism of a child of Robert Mackintosh, son (by a first marriage) of Lachlan Mackintosh of Strone, whose second wife was Christian Dallas, the laird's mother."
Sources
The father of Crystal Hall used google, yahoo, family search, find a grave, and ancestry.
Dallas, James. The history of the family of Dallas. Printed by T. and A. Constable Ltd., Edinburgh. 1921. pages 172, 178, and 290