The noun (Substantiv/Nomen) Vertriebene is feminine in German. Therefore, the correct definite article in the nominative singular is die. So, you say: die Vertriebene.
displaced people
Menschen, die aus ihrer Heimat vertrieben wurden.
People who have been displaced from their homeland.
Die Vertriebenen wurden in Lagern untergebracht.
The displaced people were housed in camps.