The tone of Kajiura's initial response had me worried about her relationship with the members. But she seems calmer and more supportive in her subsequent tweets, so I guess the reunion shouldn't be controversial

Yeah. I think it just dragged up bad memories for her, and if she's still angry with anyone, it's the agency. They're not obliged to involve her, but it would have been polite to at least tell her that it's happening. Lots of people would ask her about it, and it was already leaked to a newspaper!