The image had been shared around the school, and the girl in question felt humiliated, even though it wasn’t her real body — if everyone thinks it’s you in the image, then it’s hard to fight that rumour mill. As to why she cared about this, well even if you, as an individual, try really hard to not care, it turns out that a lot of people do care. A lot of people called her a slut for taking such provocative images of herself, even if that’s not actually what happened.
This goes beyond the deep fake side of things. I know someone whose ex distributed nudes that she had sent to him (revenge porn, basically), and it led to her being fired from her job. The problem here is that it’s not always the individual whose nudes (or faked nudes) are shared who has the biggest problem with that person being seen naked.
Okay then the logical step to take is to educate the population about the possibility of nude images being AI generated.