Her enmity is largely understandable and justified, she could be a bit more forgiving
Her negative feelings for Mishio are indeed understandable, but understanding and justification are not synonyms. Only way Mishio can be held accountable for Rika's suicide is if she psychologically and/or physically bullied her into it. Like, what the hell, the bitch nurse purposefully used someone's suicide to make a student miserable, how in the world is that justified?? Also, "forgiving". What should she forgive? Granted, we do not know the details, but again, unless Mishio bullied the teacher into suicide (and let us be honest, does anyone see this as even remotely possible?), she is not responsible the latter offed herself, there is nothing to forgive.
The nurse's feelings are understandable, even nothing out of the ordinary with regards to the situation, but she still behaved like a massive cunt, and was not justified in doing so at any point. If you are an asshole towards someone because you have genuine emotional issues, you are still an asshole.
Also, Ena, what the fuck?! Where did that bravado from chapter 5 go?
"'Make-believe love. Make-believe!!' What an awful thing to say!! What's with her!?"
But now, suddenly, chapter 7 happens.
Oh, I just love it when a character starts over-analysing what someone obviously malicious said to them, and they get a sudden rush of shit to the brain. And of course, they do not talk about it with their lover, instead they start keeping distance, GUARANTEEING their lover will misinterpret them. Because Japanese people are emotional morons, with how often something like this crops up, this must be an actual quirk. "If presented with something troubling distance yourself, heavens forbid you try talking about it, oh, and if you are worried about someone and want to protect them, ignore them or behave like a total dick to them, BECAUSE OF COURSE, WHY THE FUCK WOULD THAT NOT WORK." (The last one is not applicable here, but I feel it is a part of the same package. A package I am sick of.)