Dido Belle and Lady Elisabeth

The Fake or Fortune programme also investigated this most wonderful double portrait from Scone castle showing the Earl of Mansfield's great-nieces Dido and Elizabeth, in the grounds of Kenwood House, where they lived, giving each almost equal pictorial importance despite the social gulf between the daughter of an enslaved mother and an aristocratic one. 
This alone would make it astonishing, but the whole lively presentation of the two sitters is notable. 
As James Mulraine wrote way back in 2014
"It is a remarkable painting. The staging implies that the two girls have been surprised by the arrival of a visitor, the viewer. Lady Elizabeth Murray composes herself according to etiquette, reading, or pretending to read, but from her smile and Dido’s barely-suppressed grin it’s clear they’ve been laughing just that moment before. More importantly, Dido has leapt to her feet, but Lady Elizabeth’s touch on her arm restrains her, as if she is saying she can sit down again. Dido is dressed in a turban like a black attendant in a painting, but they seem more like sisters."

That idea/illusion surely marked a breach in etiquette that must have been endorsed by the Murrays, and presumably also by Mansfield, who paid for the portrait.
F or F did a good job in locating the £200 payment in Mansfield's accounts, although I am surprised that this had not been done earlier, as it's the obvious source. Furthermore, the payment identified the artist as David Martin (1737-1797), pupil and colleague of Allan Ramsay, the foremost Scottish portraitist.
There seems to be some ongoing debate about this identification, but it is eminently defensible.

Other, independent research by Etienne Daly conjecturally identified Dido's turban with  one presented to her father Sir John Lindsay, who as well as his naval career in the Atlantic and Caribbean, was posted to India in 1769.   He is said to have received from Walla Jaha the ruler of Arcot Amir ul Hind,   a dress of gold brocade, an inscribed ring and a turban, the last of which may be  the jewelled turban that Dido is shown wearing, with an additional black ostrich feather to put it at the forefront of European fashion. 

As it happens,  Dido Belle and Elizabeth Murray are not the only eighteenth century portrait sitters to have been thus depicted as a pair.   But these two below are clearly mistress and maid, although the latter also wears a black ostrich feather and has laid her hand familiarly on her companion's shoulder.   Is there any information on this painting?