Sarah was born before 1774. She was the daughter of William Alcock. She passed away in 1842.
"England, Derbyshire, Church of England Parish Registers, 1537-1918," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:KBD5-N5H : 30 November 2017), Sarah Slater, 23 Jan 1774; citing 23 Jan 1774; citing Christening, Duffield, Duffield, Derbyshire, England, Derbyshire Record Office, England; FHL microfilm 1,041,429.
GRO death index June quarter 1842, Belper district, volume 19 page 326 Sarah SPENDLOVE aged 69