Field's description fits the brooch below, which was photographed for Angela Kelly's book.
The earliest date I could find for QEII wearing this brooch is February 1943 when she and Princess Margaret attended the wedding of Lady Anne Spencer.
The 1943 photos are not 100% clear, but I believe that they show this brooch being worn.
The 3 photos immediately below are from the wedding of Lady Anne
In May 1943 QEII wore it when she attended a meeting at a children's hospital.
The clearest image I could find of this brooch in the 1940s comes from 1946.
Has anyone ever seen this brooch worn in more recent times?