We can clearly see Eiko's influence over Shion.
BTW, Tsuzu had already met Shion and Hiroe back in chapter 77, so this is why she found out so easily this chapter.
To anyone interested, the Manga Time Kirara Twitter account posted a clean (though lower resolution, but you can always waifu2x it) version of the comments page illustration:
(it certainly helped at redrawing that page).