In the 1841 Fulbourn census, she is aged 25, which appears to be the usual rounding of age. Also with her are five children,between ages of 2 and 11. No sign of John, so I guess it was him who died in 1839.
Sarah married John Littlechild, son of John Littlechild and Elizabeth Miller, on 29 May 1826 in Fulbourn, Cambs. (John Littlechild was born on 19 Jun 1808 in Fulbourn, Cambs and died in 1837 in Fulbourn, Cambs.)