AP English Literatur

Passage:
"The ballroom was a whirl of color and sound. Crystal chandeliers sparkled overhead, and the floor was crowded with dancers in elegant gowns and suits. At the edge of the room stood a woman, her arms crossed and her expression unreadable. She watched the dancers with a faint smile, but her eyes betrayed a hint of sadness."

Which part of the passage primarily describes the character?