There's echoes of this chapter in serialized ch7, with Natalia accepting Sara did trick her and still choosing to trust her. One of my favorite scenes in the serialized version so far, the way it's framed with Natalia shutting her eyes as she slowly accepts the truth.
This chapter also has one of Kamejiro's favorite panels top right on page 4, which was remade with a whole lot more Saras in the serialized volume 1 extras.
Also uhh yeah it's kind of a dark fantasy series. When Snake Princess talks about keeping the peace at all costs in the serialized version, this is what she means. And yes the butterfly is calling for help in mangled speech. It's unclear if it's just mimicking what it ate, but those are also tears from its eyes.