I really hate her but I think there's a good point of her showing up.
http://www.mangago.zone/home/mangatopic/1364741/
Yeah, I get what you mean. It's a very personal opinion but, I don't think Takarai is only planning bringing her back just to force the situation and make Shirotani speaks about his past. I think there's more drama to come (and maybe I'm being too pretentious to say this, since I'm not qualified as an literary expert ha! Hell no, just a very ignorant reader) and could be unnecessary drama. Anyway, I trust Takarai, maybe she have something hidden in her sleeve and this woman appearing from nowhere could be a good plot twist (crossing fingers for it tbh)
I mean, I trust the mangaka, all right? But why bring this character back at this instance of the story? What good it makes to the plot? The only thing I hope it results from this encounter is that Shiro can reconnect somehow with his old man. It seems that, bringing her back is the excuse to Shiro confessing his traumatic episode with her to Kurose, because, to be honest, this story is too good to fall in the predictable episode with her being an obstacle in the development of Shiro and Kuro's relationship. I hope not. I'll wait patiently, or I hope she got hit by a bus before going with them to whatever place they're going. (╬￣皿￣)凸