As I mentioned a short while ago, I had found only one photo of the Marchioness of Abergavenny wearing a tiara where she is identified.
That was this photo of QEII in Jamaica in 1966.
The Marchioness was listed as being in attendance on QEII for this trip, so I think it is safe to assume the lady is her. (It seems to me that the lady behind QEII is not Mary Morrison, the other Lady-in-Waiting on the trip).
QEII's Household for the Caribbean trip in 1966
By cross checking who accompanied QEII to the Opening of Parliament in various years against photos (where available), it is possible to see the Marchioness; however none of the photos is of sufficient quality to see the details of her tiara.
1982.
1984
I also found this image. The Marchioness was listed as QEII's Lady-in-Waiting in 1962.
I am reasonably confident that the Marchioness was wearing the same tiara in 1966, 1984 and 1962.
So far, I haven't been able to discover whether this tiara belonged to the Abergavenny family.
To my eye it bears a remarkable resemblance to the one worn by Lady Mount Garret in 1937.
Viscountess Mount Garret
