Hello again Magic
Have you looked at the 1881 UK census ... for Isaac ?
He's living in Norfolk with wife Elizabeth and baby Isaac (9 months) ... and surprise ... there is also a daughter recorded as
"Harriet F. - aged 4 years". 
Without being able to view the passenger list of the "Famnoth - 1883", it's diffcult to know the children who accompanied Isaac and Elizabeth Ann.
I think I have found Harriet in New Zealand - a death recorded in 1890 - aged 13 years. I suspect too, that there was also another daughter born to this couple before they left England ?
Still investigating.

Lu