In Sophocles' Antigone, Antigone and Ismene's brothers (sons of Oedipus) have died fighting each other, but while Eteocles fought for Thebes, Polyneices fought against Thebes, for Argos. Creon (Oedipus' brother-in-law, and Antigone and Ismene's uncle) gives Eteocles an honorable burial, but refuses to do so for Polyneices because he fought for the enemy. Creon also declares that no one else is allowed to bury Polyneices, and if anyone tries, he will be killed. Antigone meets secretly with Ismene to discuss burying their brother anyway, but Ismene dares not defy the King. Antigone believes she owes it not only to her brother, but that the gods have required, in the old laws, that the burial must be carried out.
By the time Antigone appears the second time, she is openly defiant of trying twice to bury her brother. She tells Creon that she owes more allegiance to the gods than to him. She is prepared to die. Ismene tries to take some of the blame as well, but Antigone will not allow it. If Ismene did not take part in the act, she feels she should not be punished for what she did not do. She is prepared to die and tells Creon not to waste time talking, since she cares nothing for what he has to say.
We see Antigone in scene one where she discusses her plans with her sister. In scene two, Creon receives the report from the Guard that someone has tried to bury Polyneices. When scene three begins, Creon asks Antigone if she is responsible for trying to bury her brother, she admits that she is, and Ismene tries to take the blame as well.
The only change I see is that where Antigone wanted Ismene's help to bury and honor their brother in the first scene, by the third scene she will not allow Ismene to take the blame for something she did not do, and decides that since Antigone has already felt dead inside for some time (losing father and mother, and now both brothers), she is ready to die.