Vashti is often called the "Deposed Queen", brave and rebellious or prudish and foolish depending on your point of view.  One this is for certain:

"On the seventh day, when the king's heart was merry with wine, he ordered Mehuman, Bizzetha, Harbona, Bigtha and Abagtha, Zethar, and Carcas, the seven chamberlains who ministered in the presence of King Ahasuerus.

To bring Vashti the queen before the king with the royal crown, to show the peoples and the princes her beauty, for she was of comely appearance.

But Queen Vashti refused to come at the king's behest which was [brought] by the hand of the chamberlains, and the king became very wroth, and his anger burnt within him." (Chapter 1, Verses 10, 11, 12)

It’s widely interpreted what kept her from coming, but one thing is clear, that if “Vashti shall not come before King Ahasuerus” the king “will give her royal position to her peer who is better than she.” (Chapter 1, Verse 9).

If you ask me, I would have disappeared too and that's exactly what happens to Vashti.  In the following video we imagine what has become of Vashti after all these years: