At this point, she's permanently scarred the Avatar in an attempt to kill him, and she's put their families in a torture facility that the Fire Nation likes to call a prison.

[ and that's not even counting what she does to advance the war, and what she attempted to do to katara during their agni kai. ]

Later, she attempted to kill all of us when trying to break them out of the prison, and the last time I saw her before she was imprisoned, she electrocuted me.

[in front of katara, but you know. he won't say that. not his story. zuko pauses ]

You can't forgive someone who doesn't even feel guilty over what they did.