Sorry to jump into this conversation so late, but this information took me a while to find. I have a list of grave stones in Boston Mills Cemetery, Chingacousy Township, Peel county, and this might help you:
#10, Catherine McNab, died Feb. 14, 1894, age 72 years, daughter of Duncan McNab and Grace Morrison of Islay
She is buried there with her husband, Robert Lawson, son of peter Lawson, of Clackmananshire, Scotland.
Also in this cemetery:
#84. Catharine J. McNab, died Mar 16, 1854, aged 20 yrs. 9 mos.
Alexander McNab, died Apr. 1836, aged 8 mos.
Duncan McNab, died April 1837, aged 9 mos.
You can see these 3 stones on Find a Grave + Ontario+Peel+Boston Mills. I don't know if or how these last 3 are related, but it's possible.
I've been looking through the names on a map of that township, I think dated 1881, but I don't see any McNabs there. However, a Robert Lawson did own land just southwest of Boston Mills. I think that the nearest church to this cemetery would be at Claude, and there might be some church records available there. Ching. is the township directly south of Caledon.