Clearing up more stuff.
The Signora stuff from last book happened, but Childe called the police, not Kazuha, she just imagined him there.
She was rejected by Kazuha, but this memory was later overwritten by her hallucinations that he said 'yes'.
She loved Childe too, but her stability wasn't that bad at that time. After Kazuha saved her, she became obsessed with him, 'cause, he was the one who saved her. And she became unstable 'cause this was the second time she got rejected.
The stuff with Scaramouche and Signora is true. However, Mel's daughter is Kazuha's girlfriend, not Lumine. Well, Lumine killed him before Scara got to him. They're still after her for unknown reasons, some sort of plan.
The investigation team stuff with Kazuha never happened, and Childe never got arrested. He was at her place all the time. But when the police came, he fled with her, bringing us to the latest chapter.
As to when Kazuha was killed, asked by a reader, Kazuha was killed in the chapter "Her Dreams" wherein she dreams she killed him, then gets comforted by him. Turns out, being comforted by Kazuha was the dream and killing him was the reality.
And yes, the 'snow' note murderer was her. She killed Lulu, many people, the Kamisato family, as well as Kaedehara Kazuha.