By addressing her as Queen Esther,
Ahasuerus showed that Esther was no ordinary citizen who had to beg for favours. No, she could ask anything she wished (although Ahasuerus’ offer of half the kingdom should probably be understood as a figure of speech rather than a literal offer).
3 And the king said to her, “What is it, Queen Esther? What is your request? It shall be given you, even to the half of my kingdom.”