Masteria Through Time - Blockbuster impressions

 Spoiler

Because she's not inherently evil. The initial implication was that she was searching for the Antellion because its power could be used to fight the Black Mage. Once things went south for her, she stopped caring about that and just wanted to prove she was right. Even after that, she still made Narcian promise to keep the Antellion in Versial, because she didn't want it to fall into the wrong hands in the maple world.

Narcian is presenting himself as the victim in the conflict, so she sees Subami as the villain (she's also obviously got the hots for Narcian, which is factoring into this). The lengths she's going through to help him are more than a bit morally bankrupt, but she's not someone who would ally with the Black Mage.

 Spoiler

If she's not evil, she should have been looking for Subani to find hints for fighting the Black Mage, rather than for Naricain who was the defeated villain (she knew he was, she said something about needing to research his fall to know how to defeat the Black Mage).
After she meets Naricain he sweet-talks her, or thinks he does. But I'm talking about what made him seek him out in the first place.