I recognized this immediately as Chinese in origin, and very distinctive of the embroidery that was done for their own clothes, and for export, in the early 20th century. Peking Knots (small knots) were an integral part of these types of embroideries that were being done before the end of the Qing Dynasty in 1911. The Clark Museum in Eureka, CA (where I worked as Textiles Curator in the mid-1980s) had a wonderful collection of early 20th cen. Chinese embroidered garments, including a beautiful paneled skirt that had many areas of this similar type embroidery. There was a significant population of Oriental immigrants to Northern California in the late 1800s, due to the demand for labor with the railroads. They brought with them the clothing from their country of origin.
The hair silks are SO fine - the embroiderers were so talented!
The couched gold threads are another clue to oriental embroideries of this time period.
I do wonder how this came about! Perhaps the panel and cuffs were made to order for this dressmaker to use. Perhaps these were remnants cut from a precious piece of fabric or from a larger, worn item. A comprehensive article on clothing manufacture and styles in the 1830s by the Conner Prairie Interactive History Park (located just outside Indianapolis) says that silk fabrics were mostly imported from China and India. Many dyestuffs and other fabrics were also imported from various countries. It's easy to forget that globalization and trade has been growing for centuries. It's far from a new dynamic of our modern era!