I also just realized it. It was so nice to reread the chapters since they found "her", it all suddenly makes sense.
All the glances from the other girls when they talk about Ruu, the fact that nobody except Yuuri and Yuki really interacts with her, the reason why the boy shot them with the crossbow (Yuuri didn't drop Ruu/the teddybear), and also the drawings Yuki did without Ruu but with the teddy instead. So many hints.