Why does antigone kill herself at the end of story?

In Sophocles' tragedy "Antigone," Antigone does not kill herself at the end of the story. She is sentenced to death by King Creon for defying his orders and burying her brother Polynices, who was considered a traitor. Antigone chooses to take her own life before the sentence can be carried out, but it is not the final event of the play.