Upgrade image posted 29 September 2016 from eBay; removed spots with Photoshop and removed residual monotone color. Also increased contrast.
The puffed sleeves and what looks like a vee-waistline suggest this image could date to the 1890s. This is possible because she was born in 1879. The card's caption also calls her Duchess Sophie Charlotte instead of Princess Eitel-Friedrich.
Keywords: Sophia Charlotte of Oldenburg, Sophie Charlotte von Oldenburg, Prinzessin Eitel Friedrich, Princess Eitel-Fritz, Princess, Oldenburg family, Hohenzollern family, German, bouffant coiffure, necklace, choker necklace, sweetheart neckline, modesty piece, bertha, quarter length puffed sleeves, ruffles, bracelets, vee waistline, fan