So both of the people who've met Satsuki seem utterly obsessed with her in a way that goes beyond way friendship. She must have been building a yuri harem.
i think that the otherside is worse at night cause most horror/ghost stories take place at night and since the otherside is basically based off these stories, more of them appear at night.
Seems plausible enough that she could keep Kozakura safe by making her look like a plant to the various horrors that might be interested in them. But if her eye has that much power, wouldn't she have noticed it earlier?