A Mary Thompson, aged about 70, was living with Sarah in 1841; this is likely to be her mother.
1841 census for York Street, Monkwearmouth:

Name	Age	Occupation
John Spain	35	Seaman
Sarah Spain	35
Mary Spain	15
Richard Spain	5
Mary Thompson	70	Widow

Sarah's ages in the censuses from 1851 to 1881 (see John) point to her being born 1804-1807. If the death certificate is for this Sarah Spain, then her age at death suggests she was born 1803-1804. A Sarah Thompson, daughter of Richard Thompson and Mary, was christened at Dundas St Independent on 19/07/1805 and, since Sarah's son Richard was christened in the same chapel and her mother is likely to have been Mary, this is likely to be her.

Durham Records Online:
Cemetery Registers, Sunderland District - Record Number: 189803.12
Location: Sunderland (Fulwell)
Cemetery: Mere Knolls Cemetery - Western Extension
Denomination: any
12 Nov 1890 Sarah Spain, of 84 Whitburn Street, age: 86, widow.

Sarah's death was registered by Margaret Knowles, grand daughter of 84 Whitburn Street, Monkwearmouth. Margaret has not yet been identified.

My 3 x great grandmother.