In The Pearl, Juana 'cries shrilly' because she is upset. This could be from several reasons in the story. First, she is upset when she realizes the Pearl does not represent good fortune. She hates it and in fact tries to save her family from its effects by throwing it back into the ocean. She also cries when her son is stricken ill, stung by a scorpion.
She began to cry shrilly when her son Coyotito had been shoted by the trackers.