(OoC: Not a traditional answer as this one was commissioned by Lego-Joker at a super discounted price, base on the Two-Face story, The Eye of the Beholder. This was a blast.)
In my headcannon, there was a parallel version of Twylight who got this way; karma for the Marer Do Well and Walking Dead hoaxes. And our Twylight faced her own darkness when facing her.