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Nice, well at least we know that there are two options about this girl. She can also be an ex trainee or from the school.
But if it's the 1st one (new FL) then I don't agree with your opinion. She doesn't bosses him around she literally is telling him the normal stuff people should actually do and not act on impulse and kill someone. She also immediately noticed the change in him and is showing concern about how different he acts now. If she was ignorant and caring only about herself she would just be happy and wouldn't pay much mind to it.
My point is... that they both have problems, they're toxic but they're also each other's safe place. I hope that everything will settle, get better and they'll be both happy after some healing period.
If the girl at the end is a new FL, I'm up for it because I can't take this current one bossing him around. He is trying but she is not even seeing his effort just caring about herself.