Getting back to the original question, the Bennet girls and the Dashwood ladies would have made some of their own things, bought others ready made, and commissioned a local dressmaker to make others.

Things like bonnets and hats were often purchased un-trimmed, and decorated to taste by the owners. Ridicules, shawls, pelerines, and scarves could be purchased ready-made, although I can certainly see the patient Jane Bennet embroidering her own ridicule.

Body linen, such as chemises, night rails, and caps, could be purchased ready-made, but the thrifty lady often made her own if time permitted. The Bingley sisters would more likely have engaged one of the upper maids to make their linens.

Having a dress made generally involved two trips: one to the drapers to purchase the fabric, and a second to the modiste to have a dress made up. (When Edmond speaks of purchasing a dress for his sister, he is most likely referring to a dress length of fabric, rather than actually purchasing a ready-to-wear dress). There would be a consultation with the modiste, and often the lady would bring with her paper patterns taken from another of her own dresses, or a copy of a friend's dress she particularly liked, etc. The dressmaker would then turn the dress length of fabric into a garment.

There is some evidence in the London newspaper advertisements of the period that many garments were available ready-made, particularly capes, mantles, robes and pelisses. Considering these garments' construction, it wouldn't have taken more than minor alterations to personalize the fit to suit the buyer.

Trimming of the garment was left to the handiwork of the wearer, in the case of someone of the Bennets' or the Dashwood's class, and ladies took great pride in devising their own personal decorations and trimming. The upper class ladies like the Bingley sisters might have had their maids do the actually sewing, but they would have been involved in the design of the decoration.

It was considered quite genteel to be involved in whitework embroidery of one's caps and capotes, a very lady-like occupation.

I could natter on for hours on this topic, but I hope this helps a bit. If you are interested in more information on making your own regency wardrobe, I humbly invite you to peruse my own website, The Regency Garderobe (if that's not too blatant a plug ). There is quite a bit of information on evolving styles, modern patterns available, etc.

Louisa
Mistress of the Garderobe