De Glehn's Wikipedia entry is here, but it is brief. Much more information can be found on this site, including some information regarding himself and Sargent (here). More information on de Glehn and his wife Jane is here.
While de Glehn can be considered an impressionist, he made many portraits that were traditional in style. His series on female nudes tended to be more sketchy, but not impressionist.
The woman is thought to be Jane, but could be someone else.
Gallery: de Glehn's Works
A website has this dated 1932, but I'd say it would be more like 1912, to judge by the clothing.
Fontanne was British, but best-known on the American stage, often appearing with her husband, Alfred Lunt.
This is the niece of Jane Emmett, de Glehn's wife.
De Glehn painted many nudes.
An example of de Glehn's landscape work.