Mrs Robinson was delighted to hear that the commendation and plaque, known as "the death penny" so-called since it was issued to the next-of-kin of soldiers killed in the war, would be back in family hands.
She recalled visiting an aunt who lived in Pukekohe many years ago.
"She had the death penny medal sitting there."
It was not known how it came to end up in Australia.
"I often wondered where it had got to."
Mrs Robinson has now been in touch with Napier RSA vice-president Joy Miller and she will be taking it up with the national office.
Private Cox had been a determined young man.
As a child he suffered rheumatic fever and tried several times to enlist but was always turned down due to his medical record.
So he journeyed to Dunedin and managed to get enlisted into the 2nd Battalion Otago Regiment and embarked for service in January 1916.
He died on his first day in battle while delivering supplies with another soldier.
A shell landed beside them killing them both.
He is buried in the Caterpillar Valley Cemetery, Longueval, France.