Yuzumori-san's face was pretty terrifying.. Poor Mimika.. (´・ ~ ・`) Like most of us here, I think that Yuzumori-san was just angry, because she misunderstood her words and thinks that Mimika lied to her and doesn't actually want to be friends with her (even though we know the reason why Mimika said that). Although, with this manga and its history of unpredictability, I'm not sure at all.
The cliffhanger, though... Ejima-sensei.. so cruel.. ;o;