Well, she's 12-13, if memory serves right. And that's basically the age where things start to happen. Plus, she's at times mature for her age (when she's not looking at poop). So granted, I'd rather she didn't think that way, but the kind of resolution she's making in her mind, "going to hell with Sugimoto"... That's something that goes beyond friendship at this point. She's becoming a young woman very quickly due to circumstance. While it's thankfully obvious that Sugimoto sees her as the girl she is, and tries to protect her like that, she's changing in that aspect, and that's a subtle subplot that I don't know if Noda can manage to do well.