John Gill Commentary Esther 1:11

"to bring Vashti the queen before the king with the crown royal, to show the peoples and the princes her beauty; for she was fair to look on." — Esther 1:11 (ASV)

To bring Vashti the queen before the king
Not against her will, or by force; but they were sent to let her know it was the king's pleasure that she should come to him immediately:

with the crown royal ;
that is, upon her head, to make her look the more grand and majestic:

to show the people and the princes her beauty ;
for she was fair to look upon; which was not wisely done, neither was it comely nor safe.