The answer came after a lot of research starting with birth death and marriage parish registers in Germany (German Genealogist), then passenger lists from Hamburg to London (Ship Capella) then Bristol to New Zealand (Ship Stonehouse). But the final clues came from one of the most fantastic websites I have used which lists births and deaths at sea on British registered ships.
The end result was a really sad story, Anna Christina lost 4 babies on the way to New Zealand had 2 babies here and died when the oldest was just 3yrds old. She lies in an unmarked grave in Oxford Cemetery (just out of Christchurch) we are searching the burial with the cemetery administrators and will be putting a headstone with:
loved daughter of ......... mother of ......... and loved wife of Peter Christian Johannsen.
Anna is not my great grandmother, Peters second wife was. But having unearthed this tragic story, Anna deserves it.http://www.bmdregisters.co.uk/