Frederica (Olava )Olsen

I had been searching for the ancestry of Olava Olsen, my maternal great grandmother. I have recently found that her name was Frederica Olava Olsen born approximately 1862 c/- Bertie Christensen, Gjettemyrs, Weien, Christiana. In New Zealand she was always known as Olava She emigrated to New Zealand on board the Arethusa from London on 1879-09-03 arriving in NZ on 1879-12-07. aged 17 and described as a Domestic Servant. I am interested in researching her ancestry. Can anyone kindly help? Don L