From 1861. Guessing here, could Marion aged 13 who showed in 1851 have died and they re-used the name? As transcribed:
Fiel Campbell 56, fisherman
Margret Campbell 40
Cathrine Campbell 20
Alexander Campbell 18
Duncan Campbell 9
Marion Campbell 7
Thadlac Lied (?spl) 60, boarder
Address: Cochskipport, Howmore, South Uist
And 1871:
Niel Campbell 65, cottar
Mary Campbell 57...a second marriage or is Marg. being read as Mary?
Alexander Campbell 30
Catharine Campbell 28
Christina Campbell 26
Marion Campbell 18, General Servant Domestic
Norman Mackay 4 grandchild
Mary Mackay 2 grandchild
Robert Munro 60, lodger
Address: Baynafaoliron, Howmore, South Uist