Her reasons for committing the sins I understand, I just don’t condone it (that’s why atonement in form of punishment is needed). She strung an innocent person into her own problems, that’s why the lying for the greater good analogy doesn’t apply here. Horuto was living a life at peace with his surroundings , at balance with the yin( strong friend group) and the yang(occasional disdain from peers). Her actions directly attack that balance, the only way to hurt Horuto was through deceit. As we the readers learnt that direct attacks don’t work on his beautiful soul. Horuto is the symbol of selflessness that’s why all sins committed against him are mortal sins and must be punished no matter the reason.