During the South African tour of 1947 QEQM began to wear some of the jewels which disappeared from public view during the war period.
Among these was her Cartier Lily brooch which she wore to a Garden Party in Pretoria. As far as I can ascertain this was the first public wearing post WWII.
Detail
Later in July 1947 HM again wore the brooch at a service for the Mothers' Union at Westminster Abbey.
And later that month for a service at St Giles Cathedral in Edinburgh.