Esther had just revealed to the king, her husband, the evil plot of his adviser to wipe out the Jews. The king quickly sided with Esther and had the adviser executed. However, his evil plan was still in place, and she wanted to stop it, or be able to counter it.
“Now Esther spoke again to the king, fell down at his feet, and implored him with tears to counteract the evil of Haman the Agagite, and the scheme which he had devised against the Jews” (Esther 8:3).
She already had the unquestioned favor of the king, nevertheless, she fell down before him, imploring with tears to counteract the wicked scheme.
Remember, Esther was a queen, yet, see her humility.