What a lovely young woman, and such a dress - simple lines in the finest shining fabric. I'm thinking silk. No wonder her dog is having all kinds of second thoughts about jumping up on her. This is Grand Duchess Alexandra Nikolaevna of Russia (1825 – 1844) portrayed in 1840 by Christina Robertson, a Scottish painter. Though Robertson is now little known, in her time she was successful by any artist's yardstick, which as you'd guess was particularly challenging for a woman, wife and mother in the early 19th century. (A biography can be found here.) So much of her success was found among the Russian royal family that she died and was buried there, despite setbacks late in her career.
As you might guess, the primary drive behind a royal portrait is to be idealized; that warts-and-all thing won't fly unless you're Goya and know you can get away with it. Alexandra was about 15 here and was by all accounts actually this beautiful, as well as animated. Imagine Christina Robertson of Fife, Scotland at age fortysomething recording such a paragon; she might have felt a lot like that lapdog, unable to touch her.
I wish I could tell you this pretty, talented girl had lived happily ever after - well, she did, for about four years. She died young along with her newborn child, within a year of her marriage, leaving many hearts shattered. Oh dear, I wish I didn't see that ending so often.