It might be just me, but even as an introvert, I find Shimamura's attitude toward her "pseudo-friendships" with "Pancho," "Delos" and "Santos" to be a bit too cold and cynical. Not all connections with other people have to be deep or lasting, but she too easily writes off those three as not worth her time instead of recognizing that they're trying to be friendly and trying to genuinely respond in kind.
I think Shimamura might actually be on the spectrum. The way she handles social interaction, and the way she thinks about things are pretty atypical. Her difficulty relating to the new girls likely stems from a incomplete grasp on the simple nuances of interpersonal relation that comes naturally to the typically-minded. Also explains why she is confused by Taru's actions and behaviors.
