A Fall into Darkness

Clark Kent has seen both sides of the human soul, But now he's met her, her long raven locks, almost black and gold eyes, he met her by accident at first he thought her to be a monster, when she is injured and his friend asks his assistance in saving her, he feels a deep connection. But it's her darkness he worries about, after 1300 years it's a long time to keep something under control she has never had to. Can he keep her darkness at bay or will be have no choice but to destroy her because of that darkness.
(alternate universe)