Bertha Thornton B1919 New Zealand

I am trying to trace the family on BERTHA THORNTON B1919 NEW ZEALAND
She was the daughter of PERCY THORNTON B1880 LANCASHIRE UK and MARY ANN CADE B1880.
She had one brother CHARLES OSWALD THORNTON B1921 New Zealand.

Bertha was the founder of MARY GRAY CHOCOLATES a handmade chocolate business in New Zealand which is still trading.

I am really trying to find out more about the business she created and more about her and her family.