First of all, Juana is an Indian in Mexico, so she maintains some of the ancient beliefs of the Indian; on the other hand, her people have been converted to Catholicism by Spanish missionaries.
In the exposition of Steinbeck's The Pearl, Juana sings an ancient song that has only three notes, but it possesses "an endless variety of interest." When her baby is bitten by the scorpion, Juana whispers "the old magic" and Kino hears "the evil music of the enemy," so they are both superstitious and primitive in some of their beliefs. For instance, when Kino looks at the Pearl of the World, in the surface of this great pearl, he can see dream forms. But, he and Juana both hear the music of evil later on when the outsiders come to see the pearl.
After Kino is not able to sell the great pearl and he is attacked, Juana tells her husband,
"Kino, this pearl is evil. Let us destroy it before it destroys us. Let us crush it between two stones. Let us--let us throw it back in the sea where it belongs. Kino, it is evil, it is evil!"
Finally, after Kino is attacked and has to flee, his brother Juan Thomas tells Kino,
"...There is a devil in this pearl. You should have sold it and passed on to the devil."
But Kino cannot part with it. As he leaves Juan Thomas, Kino tells his brother, "This pearl has become my soul. Go thou also with God." Later, as the trackers come near him, Juana cautiously looks through a hole. She
whispered her combination of prayer and magic, her Hail Marys and her ancient intercession, against the black unhuman things.
And, then, when the evil overtakes them and Coyotito is dead, Kino and Juana throw the great pearl. It lands on the floor of the sea, buried is sand.