Hello Myshell
The 1841 has Sarah (aged 7) living in Grays, Thurrock with her parents but it does only state Essex as her place of birth not Grays, Thurrock and her parents Robert & Sarah have a N by whether born in same County so they were born somewhere else?
The 1841 census will tell you if an individual is born of the County that they are living in by means of Yes/Y or if they are not born of the County they are living in by means of No/N.
Grays, Thurrock is by the River Thames, South Ockendon is two or three miles north of Grays.
In 1851 Sarah is aged 18 and working as a house servant in Gravesend, Kent which is just across the River Thames from Grays and was easily accessible by ferry. Sarah's stated place of birth is Gays (Grays)Thurrock, Essex
It looks like Robert Mansfield may have died Mar qtr 1848, Orsett R.D and its possible that Sarah Ann Mansfield (his wife) may have got married again in Gravesend to a William Robert Jewiss on the 10th Dec 1850 at St Georges, Gravesend
Bryant