Welcome to Rootschat
I think you're mixing the two Sarahs. It was the second Sarah, Haynes, who was born on 27 Oct 1818 at Kempston, Beds, parents Thomas and Elizabeth.
Sarah Tearle would have been born earlier than 1818 to have married in 1832, and there are no Tearles in Kempston. The question is, who was she? I can't find her burial 1832-40, nor a death 1837-40. As there were no other children I suspect she may have died nearer to 1833 than 1840. The family appears to have been non-conformist so perhaps Sarah Tearle wasn't baptised at all in the established church. No obvious baptism or burial is going to make it difficult. Have you checked the 1832 marriage to see what other detail is included eg parish of residence and witnesses?
David