This may be her death - Durham Records Online:
Burials, Sunderland District - Record Number: 538041.2
Location: Sunderland
Church: Holy Trinity
Denomination: Anglican
17 Apr 1845 Mary Watson, of Long Bank, age: 80, died 13 Apr 1845, widow of William Watson (harbour master for Seaham).

...in which case, the 1841 census for Dawdon, Seaham Harbour is of interest:

Name	Age	Occupation	whether born in the county
Mary Watson	77	Widow	Yes
Mary Jane Minto	13		Yes

A Mary Watson married a Christopher Minto in Sunderland on 01/01/1828; I suspect this is Mary's daughter born 1805. Mary and Christopher had a daughter Mary Jane born 24/10/1828, who is almost certainly the 13 year old Mary Jane Minto recorded with her 77 year old grandmother in the 1841 census.

One of Mary's grandchildren, Christopher appears in the 1851 census to have a middle name of Mento, however given the evidence above I suspect he is named after his uncle Christopher Minto.

My 4 x great grandmother.