What emerald and diamond necklace are you referring to? As far as I am awawe, Camilla does not have any emeralds with a Greville provenance.
As regards the ruby neckalce worn by the Queen, she received it as a wedding present from her parents. She has not worn it since the 1970s.
Both her engagement ring which is emerald & diamonds and the necklace which she has worn as a 3-string at at least one banquet are from the Greville gift to the QM.