I believe the date of birth indicated on Rachel’s death certificate and gravestone to be off by one year  . I determined her year of birth to be 1808 by the following factors.
Rachel’s brother, Jeremiah, was born July 27 1806.  In order for Rachel to be born February 26, 1807, her mother would have had to become pregnant almost immediately after giving birth to Jeremiah and given birth to Rachel 2 months premature. Therefore, it is my conclusion that the year of 1807 is incorrect.
The Canadian censuses of 1851, 1871, and 1881 give a better clue of Rachel’s year of birth.
The 1851 census for New Brunswick and Nova Scotia was completed in 1851, but Canada West and Canada East did not start their collection of data until the following year. Therefore, for Canada West and Canada East, what is known as the Census of 1851 officially began on January 12, 1852. The census inquires the age at the NEXT birthday. Rachel gives this information herself (as indicated by the X next to her name) as 44. Depending on when the census was taken (before or after her birthday in February), her year of birth would calculate to 1808-1809. 
The 1871 Census officially began April 2, 1871. It asked for current age. Rachel’s age is given as 63. She had already had her birthday, so year of birth calculates to 1808. 
The 1881 Census officially began April 4, 1881. It again, asked for current age. Rachel’s age is given as 73, which would calculate year of birth to be 1808.