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.