We're told that Celia only has only removed the drop pearl earrings from her ears nine times to clean them, and that nobody remembers having seen her without them—ever. Even Pilar can't think of her grandmother without seeing those pearl earrings in her mind's eye, and they are the first thing she looks for when she sees her grandmother again in Cuba.
It's clear that García wants us to connect Celia intimately with her beloved jewelry. She uses the earrings as a type of heraldry for her, with the pearls acting as outward signs of her long-lost passion for Gustavo. She continues to wear the pearls not as a sign that she still longs for Gustavo, but as a sign that she desires a life of strong feelings and a deep communion with the people she loves.
When Celia releases her earrings to the sea, it's as though she's letting a major part of herself fall away into the darkness. Does it mean that she's ready for death? Or perhaps she's ready to reinvent herself? Yes to both of those things.