Census data is sometimes not what it seems.
Elizabeth was Margaret's mother and can be follwed through the censuses to:

1851, Patrick, district 2, schedule 85, Ballahutchin
John Quilliam, head, married, 45, farmer of 89ac employing 4 labourers, Patrick
Elizabeth, wife, married, 47, Patrick
John, son, unmarried, 23, farmer's son, Patrick
Catherine, daughter, unmarried, 22, farmer's daughter, Patrick
Elizabeth, daughter, unmarried, 20, Patrick
James, son, unmarried, 11, scholar, Patrick
Henry, son, 9, scholar, Patrick
Ann, daughter, 7, scholar, Patrick
Margaret Callin, daughter, married, 25, farmer's wife, Patrick
William, son in law, married, 27, farmer, Patrick
plus 3 servants