It was only the recent death of Mrs Gray, at the age of 90, that stopped the flow of letters, Mrs Forbes (91) said.
Through the years, the letters contained a chronicle of the two women's lives, from the war years, to marriage, to having children to grandchildren and beyond.
"All through the war we kept in touch," Mrs Forbes said.
Mrs Gray kept all the letters Mrs Forbes wrote to her.
The writing relationship began when Mrs Forbes answered Mrs Gray's request for a penfriend in a magazine.
Mrs Gray lived in Orlando.
"We never stopped [corresponding]. There was always a letter from Edith," she said.
The two women developed a close bond over the years and in 1971 Mrs Forbes went on a Country Women's Institute (CWI) trip to the United States and took some time to visit Mrs Gray.
At the airport she wondered how they would recognise each other, she recalled.
"As soon as we saw each other we knew each other," she said.
"I was greeted with great warmth and it was as if we had known each other all our lives," Mrs Forbes wrote in a CWI report when she returned.
"What a wonderful time I had with the Gray family - I stayed 10 days and every day was exciting, meeting their friends," she said in the report.
Then in 1978, Mrs Gray visited Mrs Forbes in New Zealand.
"So I haven't seen her since then," Mrs Forbes said.
Not only were the two women good friends, but over the years people had remarked how much alike they looked.
So when the news came that Mrs Gray had died, Mrs Forbes, who is now a resident of Cameron House rest-home, in Gore, described her friend's death as like losing a sister.
Ironically, for the avid letter writer, Mrs Forbes learned about her friend's death through a letter from Mrs Gray's daughter, which began: "This is probably the most difficult letter I have ever had to write".
