I definitely do think the religious girl is somewhat mentally broken. She's a good example of not being able to deal with memory retaining reincarnation. It wouldn't surprise me if she could deal with it so badly that it's the very reason she was abandoned by her parents. Maybe she started talking "nonsense" to the parents about Japan and whatnot, and the parents were worried and ultimately horrified enough to abandon her. They might have thought she's possessed. She's also the perfect candidate for religious brainwashing if she can't deal with reality and thus needs something extremely solid and unquestionable to rely on, which is typically a god/religion. Under such circumstances, it makes more than perfect sense for her to view the system voice as the voice of a god. Along the lines DarthEnderX said, she would naturally go out of her way to interpret everything she heard and saw from a point of view that reinforces the faith she needs for (psychological) survival.