Whether or not Iphy is the passive twin is debatable. It's strongly hinted as the story progresses that she's truly the strong-willed one, possibly very manipulative of Elly all along. Much of the account is given to us from the distorted lens of Oly, an extremely unreliable narrator.

It's all Oly (aside from the reporter's entries, etc.). The reason it's so disjointed and jarring is that Oly is FUCKING CRAZY. Way more crazy that is on the surface of her narration.

I must have missed that. But the logic seems faulty. If she takes these girls who are freaks, and then removes what makes them freaks and allows them to "feel beautiful"—presumably a new feeling for them—wouldn't it be harder to convince them to then scar themselves all over again?

I wrote about this a bit in my own huge wall of text elsewhere, but I think that not only does Oly kill Miss Lick because she never acted in her family's defense from Arty's machinations (no one did), but also because she always secretly hated Arty and wanted to murder him herself. She was his abused slave. His Igor.…

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"Miss Lick, 'saving' the exceptional by making them ordinary"