How is Antigone's fate forshadowed during her opening scene with Ismene in Antigone?
You are right in identifying that in this play, as in Oedipus Rex, Sophocles uses an immense amount of foreshadowing to plant clues or hints about what is to happen later on in the play. In this opening conversation, therefore, we see many indications of the death that awaits Antigone as she seeks to do what is right before the gods rather than before the edicts of man. Perhaps most telling is her first speech to Ismene, which ends as follows:
What, haven't you heard? Don't you see?
The doom reserved for enemies
Marches on the ones we love the most.
Here we see that Antigone comments on the twist of fate that has led her brother, dearer to her than anyone, to be considered as an "enemy" and treated as such. And yet, Antigone will also be considered an "enemy" for her disobedience of Creon's edict and will suffer the same "doom" that enemies normally face.