A few bits on Margaret McIntosh and her family ...
I think her birth registered at Kirriemuir 16 Apr 1858 as 'Margaret Peter Finlay', mother Janet Finlay, no father listed - this from IGI, check out original on SP to be sure
1861 census - as you had found - Margaret McIntosh living with her Great Aunt, Margaret Peter, Alexander Findlay, Janet Find/lay her mother, in Kirk Wynd, Kirriemuir
1865 - Janet Find/lay marries William Peacock in Dundee, they have a daughter Barbara Duncan Peacock (see Ancestry for family trees for her)
1866 - Janet Find/lay Peacock, mother of 'your' Margaret McIntosh dies in Dundee