Could this be Elizabeth the year before they married?
Patrick Foy, 61, Cloth Hawker from Ireland
Anne his wife is 56
Children:
Michael 27, b Kirkham Lancashire, Cloth Hawker
Sarah 25, also born Kirkham
Sarah 22, Elizabeth 20, both born Poulton le Fylde (near Preston)
All 3 girls are Cotton Winders
Patrick 12, already a Linen Worker, was born in Preston
They live in Bedford Street, Preston
ps - there is another Elizabeth Foy in Preston, who was born about 1849, nearer your supposed age for her than the Elizabeth above.
The reason I wonder about the one above is because the b.1849 Elizabeth continues to appear in the census in 1881 and 1891 and from what you say yours had married Wilfred and headed to NZ?