According to her Wikipedia article, Pilar barely got past her eighteenth birthday. The family resemblance to her sisters is evident.
From Wikipedia; a small number of spots throughout image were removed with Photoshop and sepia tone removed by gogm.
Details of late 70s coiffure, jacket, and chemisette are evident in this print of Infanta Maria del Pilar.
Keywords: 1879, Infanta Maria del Pilar, Princess, Borbón family, Spanish, long straight coiffure, chemisette, high neckline, ruff, bow tie, jacket, lapels, ruffle, earrings