Me again! I tried to look for her in 1841 to see if it held any clues. There were so many Sarah Knights of that age it was hard to decide. Is she the one married to Robert, a rope maker? If so, one of the sons seems to have a very odd name so that might be a clue. Merick?
Can you quote the census reference so we can look at the right one? Had she died before 1851? Do you have the death certificate?
Andrea