Sarah's father registered her birth on Dec. 5, 1870.  The 1901 census has her date of birth listed as Nov. 27, 1870.
Ontario, Canada Births, 1869-1907 Record info about Sarah Mcarthur
Name: Sarah Mcarthur Date of Birth: 27 Nov 1870 Gender: Female Birth County: Wellington Father's Name: James McArthur Mother's Name: Mary Rodwell Roll Number: MS929_3

Registration #012141. 27 Nov. 1870. Sarah McARTHUR, female. Father James McARTHUR, accountant. Mother Mary NODWELL. Informant James McArthur, accountant, Hillsburg. Registered 5 Dec. Accoucheur Dr. Burnham. Registrar Charles Ferguson, Division Erin, County Wellington