I tend to agree with nothingsp.
My personal dislike of Zoe as a character does not take away her importance to the story at the early stages.
Actually she was very interesting at the start and was the reason I made Haru to see how their interaction would go. Needless to say I was quite distressed and 2 years later it's still a sore spot when I think back on it. (I havn't gone back and re read so maybe it's not as bad as I remember)
I didn't wan't the same thing to happen to Lilly and it was so close to happening a few times. I made her the story of the struggle and striver to be more despite being among the weak (initially), and to have the compassion and drive to continue that journey. I know I risked her being a Mary Su there, but I think overall it went okay with good development and character growth.
Still Zoe is who she is and I'm sure she was up to certain things that might instigate the sequel ;) maybe messing with the magic circles stuff.