If you are wanting assistance of a forum to add to your knowledge of Helena Roberts and her origins, and the later life of her parents and siblings, the information contained in her marriage and death certificates will be useful.
I am reading your initial enquiry to include her family, and specifically, the circumstances of her arrival in NZ.
"....Any ideas who she came to NZ with as I have no records here to check at the moment."
"...I also have no information on whether or not Edward and Mary Ann emigrated to Australia from the UK before or even if they came to NZ with their daughter.."
A marriage certificate would have witnesses, who might quite likely be a close relative...sibling or parent. It should have name of parents, including mother's maiden name. You are giving this as "..possibly Cornfield", so daughter's marriage certificate might give you a name.
If it identifies a church, that church might be where any brothers/sisters in NZ might also marry.
Marriage or death certificate might give occupation of her father. If it is a trade, then sons might have same occupation, which could assist in locating them, if they also lived in NZ.
Because you are looking to confirm details such as place and year of birth, and you have an indication of a year of arrival, and her age, I was wondering if this had come from a death certificate. If it had then it is worth considering that death certificate information can be less that accurate, in which case the year of arrival, and age, might be out by a few years.
A death certificate will give a place of burial. If other family went to NZ with her, they might also have died and be buried in the area, even same cemetery.
