Those are often referred to as a boudoir cap or lingerie cap. Many were home made which your might be and which makes accurate dating a bit difficult. These were poplar in the Edwardian era and well into the 1920s. Yours might be WWI 'Teens era. They were not usually worn while sleeping as they are rather delicate, but were worn around the home in the morning or late evening, or while dressing/lounging in one's boudoir or bedroom. Very pretty.
