This miniature portrait of an unknown young lady has been attributed to Lawrence Sully (1769-1804). Sully was not a good artist, and many of his miniatures are somewhat primitive in style. Nevertheless, he was one of a small group of miniature painters active in late 18C USA.
An interesting aspect of the miniature is the sophisticated frame, in gold with an intricate hair-work reverse.
With Sully dying in 1804, this is unlikely to date later than 1804. It shows that at that time, case making skills in USA were the match of those in Britain (although in this instance the bezel and hence glass are loose).
Some cases and parts were imported from Britain at this point, so it can be difficult to tell British and American cases apart.
However, by two years later, in 1806, there was a complete divergence of style.
British cases continued in a similar manner as this one, until the change to cabinet, or rectangular, miniatures around 1810-1815.
Whereas, in America, the ability to import cases and parts was adversely impacted by the trade wars relating to the American Embargo Act in various forms, resulting in the War with Britain.
Thus, American case makers had to rely on available materials and thus developed a new style, with a small window at the rear and where most miniatures were opened from the front.
I wrote about the impact of the Embargo Act on American casework a couple of years ago at 2008 - Additions and Comment: Case study - The Embargo Act of 1807 ...
There is more about Lawrence Sully and another miniature attributed to him at View 1374