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
Duchess Elizabeth N. Obolensky clothes off in the century (my note: appears tobe colorized portrait from 1903 Romanov ball. Nice though: pose minimizes the BelleEpoch fit, makes it look more accurate. Letnik over rubakha, ozherlya, ubrus, kokoshnik.