1841 and 1861 census combined with family records; once there was no sign of her on findmypast as "Sarah Dixon" (with name variants) in England or born in London, but by 2015 she is better documented, with clear record of marriage.
1861 census (as Sarah Houlton)
Birth years for the first four are estimated because the 1841 census rounded ages to multiples of 5 years from 15 on. Young Joseph became a surgeon, working from the same address as his father. Susanna was still unmarried at the 1861 census; her later hospital admission record shows her second name definitely "Houlton", as do family records.