Gossamer by Lois Lowry

where Thin Elderly had gone to join them, it was dark. "Yes," she said, a little uncertainly, "I'm fine. Just adjusting."
    Then, recalling what he had said, she turned to him eagerly. "What's my surprise?"
    Most Ancient turned and reached for something that was behind him. He picked it up and placed it in her arms, and it looked up at her with wide, curious eyes. It was what she had once been: tiny, a wisp of a thing, with a mischievous smile and a trusting, visible heart.
    "Oh!" she cried. She hugged it to her, against her badge. "What's its name?"

    "Ask it," Most Ancient suggested.
    "Who are you?" she asked the diminutive, transparent creature in her arms, keeping her voice calm and quiet so that it wouldn't be scared.
    "New Littlest," it told her.
    She was puzzled and almost frightened at first. Then she thought, Of course! Most Ancient could not always have been Most Ancient, and Thin Elderly must once have been something else. Even Fastidious—well, maybe not. Perhaps she had always been Fastidious.
    She cradled New Littlest, moving her hands as gently as possible around the fragile little thing, and turned back to ask Most Ancient what she needed to know.
    "Who am I now?"
    "Gossamer," he told her.