What does Zelda begin studying in Paris that becomes a symbol of happiness in the book, Z: A Novel of Zelda Fitzgerald?

Ballet becomes a symbol of happiness for Zelda, as it is a way for her to escape the unhappiness in her life. By dedicating herself to dance, Zelda is able to momentarily forget about the conflict within her marriage. Ballet also reminds Zelda of her childhood, as she was a ballerina before meeting and marrying Scott. Thus, Zelda associates ballet with fond memories, and turns to it in her time of need.