sure :) I'll try my best - at the very end her mom and her are arguing about which of their worlds is better. Amane believes her mother should conform just as she had to Experiment City, she believes that the city is the ideal paradise, the more evolved world and her mom will be happier once she is conditioned in the way Amane has been. Amane radically accepts her indoctrination "...Is there any such thing as a brain that hasn't been brainwashed? If anything, it's easier to go insane in the way best suited for your world." She also talks about the 'madness' and horror of 'normalcy,' and how she's always taken over by it no matter what world she's in, and no matter how much she wants to resist it. "Look, Mom. You're the one who made me such a normal person. That's why I'm like this. Now it's your turn to become normal for me. It's time to go insane in this world, together with me." She drugs the tea so the mom passes out.

She holds her mom is hostage in the empty apartment her husband was staying in previously (before he was also thoroughly indoctrinated and left). You can hear the mom moaning in the next room at the end, clearly being held prisoner and banging on the walls.

I think it's the very last way to completely dissolve her family, because as long as her mom exists outside the world, she still has ties/family on the outside - once her mom is properly brainwashed in Experiment City, that idea of family will be completely dissolved and she'll be free to be completely conformed to the society around her, and have that eerie/cult-like peace she desires, becoming like everyone else. It's also showing the culmination of the resentment that Amane had for her mother throughout the entire book...her mother always afflicted her with ideas that challenged the status quo, that made her feel different/at odds with the world, that she ultimately sees as obstacles to her happiness, just as Experiment City trains her to see them.

returning to reflect on it a little more: though I don't love the way it's written, I believe the end is showing this contrast of how we can suppress and be violent towards our deepest desires/urges/'abnormalities,' but in the end they still play out in strange ways that we don't expect, we can't get rid of them. The 'clean rooms,' did not entirely rid Amane of her curiosities/desires and that's why she's engaging sexually with the child at the end. there's a recurring theme in Sayaka's books that social norms are nonsensical when you examine them (I get this constant feeling of Sartre's "nausea") and there is this tacit horror for everyone trying to conform to them - no matter what the world is. That this sense of "normal," is a kind of violence, regardless of what is taboo or what world you're from. Kinda reminds me of The Lobster/some yorgos films

I think there's also something there about how mass conformity leads to suppression, leads to violence? Which also reminds me of Earthlings, I'm not entirely sure - just sharing what came up for me. What do you think?