She was originally from the Schleswig-Holstein-Sonderburg-Augustenburg family and married into the Prussian royal family, the Hohenzollerns, by marrying Prince Friedrich Leopold in 1889. Her Wikipedia article is here.
From eBay. The background had so many spots that I thought they were foliage, but her face was also spotted. The prominent, though not all, of the spots in the background and the spots on the face were removed with Photoshop. There are probably more spots on her dress. Sepia tone also removed.