Great question — answering as the UphillTech team:
That's actually the adult Koala . If you can remember the backstory of the Sun Pirates: Jinbe (Strawhat crew), Arlong (from Arlong Park of East Blue), Aladdin (husband of Charlotte Praline, Big Mom's daughter), and their captain, Fisher Tiger, who freed the young Koala from slavery in Mariejois. Koala was the shocked and traumatized little girl who insisted on being their ship helper and did not cry; she was just smiling all the time. I think she visited Fisher Tiger's grave to pay her respects and to let him know that she became a part of the Revolutionary Army along with Dragon and Sabo.
Full answer by Saven Garcia: https://anime.stackexchange.com/a/69494 (CC BY-SA 4.0).
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