] Then her portrait, as Darcy's and Wickham's miniatures, was taken 8 years ago.

So where exactly does that put Georgian's portrait? 8 years prior to 1803, or 1795?

If that's the case, then her portrait is off, in the style of her garments. The sleeves are entirely wrong: those long, droopy, puff-topped white sleeves don't actually appear until closer to 1815. They're much different from the "chemise a la reine" sleeves that appear circa 1790, which are sometimes puffed at intervals all down the arm.

(I wonder if the P&P painter didn't have a copy of "In Royal Fashion," a book published by the Museum of London. There is a photograph in that book of an 1817 Russian gown worn over a white habit shirt with sleeves just like these...)

In 1795, Georgiana's gown should more reasonably have tighter sleeves that reach to the elbow; there should be very little gathering at the top of the sleeve cap as well. If she were an older woman, rather than a well-developed child of 16, she might have been painted in the Grecian mode, with completely bare arms in something resembling a romanticized chiton or tunic dress.

Here's a link to some images on my website that illustrate the pre-1800 fashions. You can clearly see a different sleeve style.

Louisa
Mistress of the Garderobe