I actually think the recently deceased Duchess is the brunette in the middle next to the blonde who I think is Lady Charlotte-Anne Montagu Douglas Scott, daughter of the 9th Duke and sister of the current Duke.
The picture must have been taken before February 1993 as this when Duchess Molly died, the logical option being in 1991 when Lady Charlotte married.
I had not seen a picture of either Duchesses Jane or Molly in their later years and so this is a first also. They were both great beauties of their generation and it is striking how elegant both ladies looked even in their later years.
Duchess Molly could give any senior royal lady a run for their money in terms of wearing incredible jewels and it is good to see that even in later life she knew how to glitter.
I presume Duchess Jane is wearing the huge emerald which sometimes was worn as a buckle to the Belt tiara.