Rops, from Belgium, sells on 8 October 2017 a "Portrait of a lady" small (36 by 29 cm) oil on panel, estimated at 3,000 to 3,600 Euro.
It is strange that they don't add anything about the artist, a she is (most likely correctly) identified on the back of the painting. Thisis a work by Jan Tilius (1653-1714), a painter who wasn't really known to me but seems to be comparable to Peter Lely (though less talented). He was also active in London from 1694 on. His works are often somewhat lifeless, and anatomically simplified. The difference with the countless high quality portrait painters of the Dutch golden age is obvious, and his works also show what an exceptional follower of Van Dyck Lely was, compared to most other artists of the period. Even so, Tilius is relatively sought after and his works have a certain charm. The knee-length is typical for him, as are the large, dark eyes.
Lempertz sold a comparable work for 10,000 Euro in 2013.
The work for sale is somewhat less attractive, so the estimate may be about right. But why they avoided the obvious attribution is not clear.