It is clear that the old woman has begun failing, feeling pain and weakness, around the time the boy goes to the American headquarters to find work. It could be the psychological result of her being aware the boy will leave her and her husband permanently once he becomes independent. In the narrative at this point in the story, Potok begins cutting back and forth quickly between the woman's activities and the boy's, as if showing them in parallel and revealing the spiritual link that has occurred between them.
At one point, in going to the nearby stream, the woman thinks of the spirit world and the interconnectedness of the streams, earth, rivers, and the sea from which water eventually finds its way back to the land and renews the system of life in the rivers all over again. This trope of a cyclic process is a metaphor of the fact of life being ongoing, infinite. It could be that the woman is contemplating the infinite, the eternal, as she leans down and feels that the spirit world is drawing her into it, down into the water, and that she will now become part of this eternal world. Either deliberately or simply inevitably, she slides into the water. Other village women pull her out; she is alive but dies later that night.
Her death can symbolically be attributed to a giving up, a feeling that she has saved the boy, who is a surrogate for the son she and the man do not have, and that there is no more for her to accomplish in this life. Or, as implied above, it could be the result of her sorrow that the boy will soon be gone. The indication was that her death from natural causes was already approaching. The cause and meaning of her death are open to wide interpretation.