Okay, all the references to the Voynich manuscript are damned cool, and since the description from the book of the pinwheel Satsuki-thing pretty much match what was drawn it seems likely that it's not just the artist picking an appropriately creepy source, it's actually what the author was referencing themselves . . .
Still not seeing how Sorawo is being selfish - what was she supposed to do otherwise? Kozakura was never going to follow her, and likewise she was never going to stay put, and even if she did come along she'd probably just add her own messed up thinking about Satsuki on top of what Toriko is going through, making it even more difficult for anyone to get out alive. "Turning her into a plant" might not actually stop anything from happening, or maybe it would - exactly how that works is pretty hard to know. It seems like trying to make a reasonable decision in a totally unreasonable situation, and even if it didn't work out and Kozakura ended up dead or something, it's not clear whether any other course of action would have changed things.