Wonderful website showing the construction and fitting of a late 18th C 'round gown' (koshka-the-cat.com) She wears it over three petticoats, stays and a cuffed shift. This is the type of 'common' dress Mary adopted.
Robe à l'Anglaise, c. 1740-1750, re-constructed 1770-1780. Cream silk, woven with a regularly repeating design of stylized flowers with the colours set up in advance in the vertical warp threads. The gown was constructed as a robe à la Francaise with a sack-back, unpicked and re-constructed as a robe à l’Anglaise in the 1770s.