Alexandra Feodorovna, Empress of All the Russias - oil on canvas - 1836 - Hermitage Museum*, Saint Petersburg
She was the eldest surviving daughter of King Frederick William III of Prussia and Louise of Mecklenburg-Strelitz, and a sister of King Frederick William III and the late German Emperor, William I of Prussia. She married Grand Duke Nicholas Pavlovich of Russia on July 13th, 1817.
(* by ‘A. Malyukov’, according to the Hermitage Digital Collection. The source doesn’t give a first name.)