The author is really good at depicting Ten's trauma in her body language. I don't want to know why they are so good at depicting deeply traumatized girls.
So Sakuya is a genuine psychopath
And possibly a narcissist who cannot get over the fact that Ten "got away".
Lowkey hate it when a character like Lulu stands their ground and is perfectly reasonable and same and then somehow gets "shaken" by the retort.
As if Lulu wouldnt just be like "pff get bent you're just jealous"
The problem is that emotions are not something you control, but something that happens to you due to an outside stimulus, and every person (who is not a psychopath, I guess) has one or two emotional weak spots that push them off balance. And Sakuya has just leveled an entire barrage of emotional manipulation techniques at Lulu, like psychopaths often do, to probe her for just such weaknesses. Even someone as centered as Lulu can be overwhelmed by this kind of assault.
That said, I am quite certain Lulu will figure out what Sakuya is doing immediately and find a way to shut her down. I would prefer it if she launched her into low-Earth orbit, too, but that's probably not on the cards...