Mindfire
Istar
However, if she's not the main character, I urge you to make it utterly unrelated to the character who is the protagonist.
If her goal in no way relates to the protagonist, how can it possibly be relevant to the plot? It'd be like she has her own separate story completely unrelated to the main one. And if that's the case, you'd be better served by just making her subplot into an actual plot for a completely different book.