looking for female cousin

Hi there, looking for my only uncles, only child. His name was Ross Mckenzie, the mothers nickname was Peggy (not sure of her real name). They had a girl, i believe she was registered as Karen Ann Mckenzie at birth. She was born in Auckland around 1961 or 1963, she was born in a home for unmarried mothers. Her mother was from Rotorua and her father (my uncle) from auckland. If anyone could help i would really appreciate it. My mother would love to find her, unfortunately my information is limited due to the fact that the family member who had the information has since passed away, leaving us no records. I believe the mothers, parents owned a boarding house on one of the main streets in Rotorua. Her fathers, parents were managers of Hotels around Northland, Waitangi and Kaikohe, their names Colin and Ruby Mckenzie. If anyone has any information no matter how small i would really appreciate it. thankyou