Looks as if Margaret died before the 1861 and David Tarbet took a new wife:
1861
61 Hilltown, Dundee
282/1 ED 23 Household No 362
David Tarbat, 50, starcher
Christina, 37,
Peter, 23, Calender
Robert, 19, Calender
Alexander, 7
Helen, 6,
Margaret, 4,
Jessie, 1