She could be just very nervous or stiff but her expressions seems a bit more cold than usual for her.

Yhis kind of makes me want to see more personality variations among the hex maniacs. Most depictions seems to basically treat HM as one person when there are multiple. A few different versions

They could all be socially awkward in different ways

one who is more like rei ayanami/yuki nagato

one who is kinda like okabe from steins gate.

they could have different hair styles and such

I think I might have actually seen something like this now that I’m thinking about it.