Bill McKeich of Paraparaumu, New Zealand, has very kindly sent me the birth certificate below of Mary Jane Marwood. It has her as being born on 11 MAR 1849 in Stanley Street, Bury, Lancashire, England. Her father is listed as Edward Marwood cork cutter and her mother as Mary (formerly McKenna). This tallies with the marriage certificate we have for Edward and Mary, which shows Edward as living in Stanley Street (see here).
The only leap of faith now is that this Edward and Mary Marwood with a daughter called Mary Jane born in Bury, is the same as the Edward and Mary Marwood with a daughter called Mary J living in Blackburn who appear a few years later in the 1851 census (see below). All the dates seem to line up between these Marwood families as does the places of birth.
1851 Census – Residence: 80 Darwen Street, Blackburn, Lancashire
Edward Marwood, head (of household) (age) 25, (status) married, (occupation) Cork Cutter, (born) Manchester Lancashire.
Mary E. Marwood, wife, 22, married, Manchester Lancashire
Mary J Marwood, daughter, unmarried, 2, Bury Lancashire
Susan Marwood, daughter, unmarried, 7 mos , Bury Lancashire
Rossthorne B. Smith, apprentice, unmarried, 17, Connenly Yorkshire
I’m not saying this is conclusive, but it’s the most credible joining of dots I’ve seen so far.