...that is a very good point. Given how Seraph is the only known psychic Crusade has, I had thought that SB was behind this via clone shenanigans as well. But if it isn't her, then there's only a few plausible scenarios that I can come up with.
1: It really was Seraph and she did it as part of a plan like you said.
2: Crusade has another psychic or someone with psytech on their payroll and they did it as part of a plan.
3: SB is having one of the other Philosophers and/or their subordinates help her with this.
4: Some rando is responsible for whatever reason.
I don't particularly like 4, just because of how vague it is, but I dislike 3 even more, as SB's psychotic rant seemed to all but outright say that she was doing this on her own and if the other Philosophers knew, they'd try to stop her, or at least sabotage her. I can't believe I'm saying this, but I really hope it was the dead woman, as that way we don't have to worry about whoever's responsible.