That's great Steve
You have confirmed what I saw earlier. If you do a children search for David Bell and Christian SELBIE, you will see amongst the other children born in Maryculter, their daughter Sarah b. 15 Dec 1838. Another daughter Christian also had an illegitimate child, Alexander in 1855.
This looks like mother and daughter Christian and grandson Alexander in 1861 - everyone born in Maryculter:
Christian Bell 68, Crofter Of 4 Acres
Christian Bell 28, dressmaker
Alexander Bell 5, grandson
Address: Wester Telbouries Croft, Maryculter
And the family in 1851, with young Sarah:
David Bell 26, Farmer (of 85 Acres-moor 100 Acres-3 Labourer)
Elizabeth Bell 24, b. Deskford, Banffshire
David Bell 2 Months
Christian Bell 58, Annuitant, mother
Mary Bell 16, sister
Elizabeth Bell 14, sister
Sarah Bell 11, sister
David Selbie 21, farm servant and four more farm servants
Address: West-telbouries, Maryculter
Jeannie's mother Sarah looks to be working as a domestic servant in 1861:
Sarah Bell, 22,House Maid Dom Servt, b. Maryculter
Address: 68 Queen Street, St Nicholas Aberdeen
Sarah is working at the McKenzie household. Stating the obvious, I wonder if that is how she met David McKenzie. Showing in the household in 1861 (everyone born in Aberdeen unless shown):
James McKenzie 54, baker, b. Auchterless, Abdnshire
Jane McKinzie 40
James McKenzie Jur 22, sailor
William McKenzie 14
Caroline McKenzie 12
Alfred McKenzie 10
Sophia McKenzie 8
Moria McKenzie 4
Orlando McKenzie 1
Willm Murray 19, baker apprentice, b. Tarves, Aberdnshire
Alexr Christie 15, b. Tarcland, Aberdnshire
Ann Gerard 26, visitor, housemaid, b. Fetteresso, Kirknshire
Monica