Seilern and Hardegg are Austro-Hungarian counties. I cannot find anything about her.
From josefnovak33's photostream on flickr; spots removed with Photoshop, image enlarged one tenth, and sepia tone removed by gogm.
This image shows little detail of the light-colored dress, but the contrasting dark lace shawl is gorgeous.
Keywords: 1865, Countess Seilern, Austrian, straight coiffure, veil, shawl, lace, crinoline