That would be Helene of Bavaria, older sister of Empress Elisabeth (Sissi). Helene was the intended bride of Franz Joseph, but he chose Sissi instead, and Helene married into the Thurn und Taxis family instead.
What a fascinating course her life has taken. The substance of the article isn't really on-topic here, but one royalty question: The article refers to her great-grandmother Crown Princess Helene. Who is that?