The 1851 census has:
Isabel Spence, 61 widow, Clothes Worker At Home b. Banff
Margaret Murray 68 lodger Formerly House Servant b. Banff
1861 and living by herself:
Isabella Spence 71 retired charwoman b. Banff
Address: 6 Double Dykes, Banff
And final one, if this connects to that 1874 death:
Isabella Spence 84 pauper (I think as mistranscrbed) b. Banff
Address: Duncan Street, Banff
Monica