There's a lot of hints towards her being the cause though. Like the bloodsigns all around the room, how she goes on and on about driving people mad, how the only ones that remain "sane" afterwards are only certain npcs (Prickett and Node aside, the only ones that remain are the Nightmares and Kuti if you don't have sex with her). Most of her covenant dialogue points to her as well. I think she also flies by on certain maps afterwards. Then again, there's not really anyway to know it before reaching her so its easy to lose everyone. I think it's a neat thing though as part of what makes the game stand out.