Symbolism, Imagery, Allegory
When Lizzie Rose starts looking around Strachan's Ghyll, she finds plenty of fine and expensive things. We're talking fur coats, silver dinnerware, and even gemstones. However, there's not much in the way of sentimental possessions. That is, until she stumbles across the picture of a smiling girl that seems like the warmest and friendliest thing in the whole grand house:
It did not seem to belong with the other pictures in the room. They were handsome but grim: dark seascapes and somber still-lifes of silver goblets and half-peeled lemons. This picture was not only frivolous but friendly. A young girl leaned toward the viewer with a puppy in her arms. Her hair fell in loose curls to her shoulders, and her lips, childishly red, were parted in a smile. (34.13)
It turns out that this is a picture of Marguerite, the only friend Cassandra ever had—and the person from whom she stole the phoenix-stone. The picture represents Cassandra's last vestiges of humanity and human connection—since falling out of touch with Marguerite, all she's known is greed, power, and loneliness.