1842-1855 Irina Vorontsova-Dashkova by Hippolyte Robillard (State Hermitage Museum - St. Petersburg Russia)
I was able to find she was born in 1835 and that she married one Fedor Ivanovich Paskevich - and that's it. That supports the tentative date of ca. 1855 by analogy to the 1853 portrait of Countess Amalia de Llano y Dotres by Madrazo y Kunz.
Replacement image posted 2 May 2014 from the Unofficial State Hermitage Museum Web site.