My guess would be that the client is wearing her shift, stays and petticoat, and that is her dress which is discarded over the chair, but she may be being fitted over the dress, and in any case, the image doesnt provide enough petticoat information to help me much: The image in the 1811-18 editions of The Book of Trades shows a clearer view of stays, and what appears to be petticoat with a tucked hem under her stays, but could be a chemise, but which doesnt provide much construction information in any case: There is this 1813 fashion plate, which also either shows a long chemise, or a petticoat worn under her stays: The lack of mention of a petticoat, when all other garments are listed, and the matching trim on chemise and hem, would indicate they were the same garment
With this costume, it's all about the hat
Stars shine bright just before twilight
Experience timeless elegance in our Elegant Black Evening Dress
Designed with adjustable spaghetti straps and a side slit
It has sleeves, which can be hard to come by with bridesmaid dresses