How certain are you about Mary's date of birth being 1840?You said c.1840, so do you think this could be her baptism?... Mary Ann LONGSTAFF Sex:F Event(s): Christening:26 Dec 1838 Auckland Saint Andrew, Durham, England Parents: Father:John LONGSTAFF Mother:Mary Batch no: P000214 (on IGI)
I know it's St. Andrew's, as opposed to St. Helen's Auckland, but they could have moved? I checked the IGI St. Andrew's for their marriage and NO JOhn Longstaffs were married anywhere near the year your looking at, which is promising. St. Helen's could have been her parish, if the marriage I posted earlier is correct: I don't know.. you'd need to verify it all, possibly via Marriage/ birth certificates.