To no one's surprise she has affinity for the rarest magics.
As a fellow author, I would've shown her affinity for light magic first... and then dark because "blackhole" so it looks a lot cooler.
On the other hand, the dark magic showing up might imply Lily has some darkness (her past life) in her that's hidden by the light (her current new life), ya know, on account of being an ex-slave, which some of us probably forgot because of all the wholesomeness.