I don't think that Mary was a pauper. I was puzzled by her place of birth being Aberdeen and her father being a shepherd. Now I know that Aberdeen might well have been more rural in the late 1820s than it was when I lived there in the 1970s but I had my doubts about shepherds

So I've investigated some more.
I checked her death cert and it is the one that anabanana suggests. She is down as widow of David McKay and her parents are as stated on her marriage cert (Farquhar McRae and Mary McRae). She died on 13 August 1915 at Temporary Hospital, Rosemount School (Usual Residence - 11 Forbes St), A David McPherson is the informant and is described as grandson.
The
1911 census has her living at 11 Forbes Street, St Machar, Aberdeen (the usual residence on her death cert) ~
168/2 56 27
Mary McKay, 80, b. Kintail, Aberdeenshire ?? (see below)
David Macpherson, boarder, 23, Tenter- Flax Factory, b. Aberdeen (grandson on death cert!)
I then rechecked the 1901 and find that I think Sancti chose the wrong Mary McKay - there were two of the same age!
This is the correct entry:
190111 Forbes Street, Rosemount, Aberdeen
168/2 50 50
David McKay, 71, general labourer, b. Creich, Sutherland
Mary McKay, wife, 69, b. Kintail, Ross-shire
David McKay, son, 13, message boy, b. Aberdeen (? is this David McPherson)
(David McPherson/McKay appears to be the grandson of David McKay.
The marriage cert of 1888 gives David as a 60 year old widower, living 61 Esslemont Avenue, Aberdeen.
David McPherson was born on 31 Oct 1887 at 61 Esslemont Avenue, Aberdeen to Alexander McPherson, general labourer and Mary Ann m.s McKay - married Dec 19 1879, Old Machar)
18915 Forbes Street, Old Machar, Aberdeen
168/2 41 22
Mary McKay, 58, general labourer's wife, b. Kintail, Ross-shire
(David might be in Clackmananshire, a mason's labourer, aged 61)
So Mary appears to have been
born Kintail, Ross-shire rather than Aberdeenshire.
One of these might well be her baptism - both IGI (extracted series)
12 August 1829, Kintail, Ross and Cromarty
Mary McRae Father: Farquhar Roy McRae
14 Feb 1832 Kintail, Ross and Cromarty
Mary McRae Father: Farquhar Roy McRae
I would think that the 1832 one is most likely, with, possibly, the first Mary dying, or would she have been baptised twice!
gnu