I'm pretty sure that whatever idea you have on what the Bane in the title means after reading the White Witch is wrong. :)
Now you can consider the possibilities before learning what it stands for.
And the more they look for answers the more questions turn up, along with some strange happenings.
We are also following Jax's fight for good to win inside her because the dealings in White Witch left her with some strange blackness inside her that is trying to turn her into a true Coven witch.
We don't get an answer to this question in Bane (whether Jax will win or not, but I'm guessing the end here cannot be dark and tragic). ;)
The thing though that I find interesting is how many people are trying to convince her it's a choice to be either good or evil when from her perspective it sounds more like she is posessed by it. I guess we'll see in the end what happens and what was the cause of the problem.
If she expells evil from her body and mind, it wasn't a choice.
In the meantime, Jax is behaving like a typical teenager and that lands her in all kinds of troubles, some small but some very big and life-changing. She is also a fleshed out character and believable (as I've been having some problems with that in the YA novels I read recently).
The problem I face now is - when is the next book coming out? As this one ended with a cliff-hanger...