Where do they find May? Is this ending inevitable or it could have been avoided? Chapter 10

They find May’s flashlight on the ground and May’s body in the river with a stone on top of her. In answer to the second part of your question, no, I don't think think May's suicide could have been avoided. Those who surrounded May were well aware of her problems, her pain, and her desire to end her pain. Her realization that the household withheld information they thought might add to her pain might have accelerated her actions, but I don't think it caused them.