When your friend is having a full on breakdown so you call her a pain and hang up, great job Shimamura.
I mean, she's shown time and again she isn't capable of dealing with these sorts of things. Shimamura is acting very much like Shimamura here. Even if it's likely the literal worst thing she could've done.
Revealed later but the reason behind Shima's answer, beside being very Shima's like, is that she don't understand most of Adachi's monologue because she was sobbing all way through it so what Shima heard was only angry sobbing shouting. I mean yes, this answer wasn't the most appropiate but tbh she don't know what could be appropriate when she don't understand a word. Also Shimamura act like nothing happen the day after.