Ismene is warning Antigone that her intended actions, to bury her brother will put her in direct conflict with King Creon's orders to leave the body to be ravaged by dogs and vultures.
While Antigone argues that her actions, or her holy crime, to bury her brother Polyneices, is worthy because she is trying to satisfy the wishes of the gods, particularly Hades who is the god of burial rites for the dead.
The implication is that Antigone will honor and obey the gods before she will submit to the rule of a mere mortal man, even if he is the King. Even though Antigone knows that burying her brother is a crime, it has a higher purpose, therefore it is a jusfiable crime.
"Antigone invokes the name of Zeus several times in the play as she defends her burial of Polyneices. Greek custom and tradition dictated that the women in the immediate family of the deceased should carry out the burial rituals, which meant that Antigone and Ismene were responsible for the burial of both of their brothers."
"When Creon orders Polyneices left unburied, Antigone felt she was acting according to the "unwritten laws" of Zeus by burying him. To her, all dead should have the honor of burial, no matter what they did in life, and she felt she was justified in fulfilling this custom and obeying the law of Zeus."