Beautiful kokoshnik with pearls! - The kokoshnik is a commonly used name for a variety of traditional Russian headdresses worn by women and girls to accompany the sarafan, primarily worn in the northern regions of Russia in the to centuries.
Russian sarafan, as the person whom I pinned this from said, it's out of period, but still lovely. According to this source: it's a Sarafan from the province of Tver.-- Reference for Princess of Russia
Russian Sarafan - It is a pinafore-like dress that hangs from under the arms down to the ankles. It used to be worn by women in Russia. It might have been derived from the panjova, another Russian garment.