So-called Portrait of <a href="https://en.wikipedia.org/wiki/en:Louise_de_K%C3%A9rouaille,_Duchess_of_Portsmouth" class="extiw" title="w:en:Louise de Kérouaille, Duchess of Portsmouth"><span title="English and French noble (1649-1734)">Louise de Keroual, Duchess of Portsmouth</span></a> (1649-1734), but it's probably a depiction of <a href="https://en.wikipedia.org/wiki/en:Elizabeth_Seymour,_Duchess_of_Somerset" class="extiw" title="w:en:Elizabeth Seymour, Duchess of Somerset"><span title="English heiress (1667-1722)">Elizabeth Seymour, Duchess of Somerset</span></a> (1667-1722)
<bdi><a href="https://en.wikipedia.org/wiki/en:Peter_Lely" class="extiw" title="w:en:Peter Lely"><span title="17th-century Dutch painter">Peter Lely</span></a>
</bdi>
circa 1670-1680
<a rel="nofollow" class="external free" href="https://collection.cmoa.org/objects/c72e80c6-8435-4c32-8655-c2e844423c7c">https://collection.cmoa.org/objects/c72e80c6-8435-4c32-8655-c2e844423c7c</a>