@Benwor - MC is surrounded by an overpowered barrier that blocks anything. Like knife stabs to the throat or rain. In this chapter, we learn it also blocks locals' ability to sense her emotions with magic. Because in this world negative emotions are a a physical thing that can be detected and even causes monsters to spawn. But MC's barrier blocks that.
Nina doesn't rely on magical emotion sense - as an otherworlder from Japan, she can just read people's facial expressions well enough to guess hidden emotions. This ability is standard in neurotypical people here on Earth, but in that fantasy world, everything is weird and magical even when it doesn't have to be, so the locals can't do it.
@tuatara1 - another important thing you should notice in this chapter is, Nina's lover has been taken from her by Sylph, an important air spirit. Looks like Sylph is going to regret stealing people's lovers.