What defeat does Marta concede in the closing section of the novel?

At the end of the novel, Marta expresses some defeat in acknowledging that without having lived it, one could never fully grasp the truths of her experiences. Nonetheless, she bears the burden of preserving the memory of Barren Shoal, as not to lose it to the obliterating forces of history and time, protecting the lives of everyone she once knew from having lived in vain.