Thanks, Ladyhawke.
You found the correct person. Mary's details from the 1851 England Census are:
Mary Delarue Age 63
Birthplace Ball, Devonshire
Relationship to Head of Household Wife
Place South Ockendon, Essex
Husband James ag lab.
I am looking for Mary Narracott's parents in Bow (or Nymet Tracey), Devonshire.