Just to give a different perspective on this...
Something similar happened at my youngest DD's school last year and one of the pictures used was of DD's best friend. This friend had been through a lot during that time. She had suffered greatly with her health (both physically and mentally) and had gone through a lot of crap at home and tbh she was very emotionally vulnerable. However she had been working hard to get better and acccording to DD she was getting better, albeit slowly. I don't really know if the school really knew to what extent she was vulnerable though.
Anyway after this incident occured her friend was devastated and yes, humiliated. She was very upset that they had done that and she kept asking DD why they would do such a thing
. Even though she had been getting better until that point she was suddenly knocked back and became withdrawn, teary, etc again.
Two days later she killed herself.
Obviously we can't say for sure, but DD is convinced that incident is what pushed her over the edge as she'd be doing fine until then and only relapsed in the two days after it happened. And tbh I do think she may be right as I also knew her friend and wouldn't be surprised if that was the case. Again can't say for sure though.
I have also worked with vulnerable teenagers myself and I could imagine them taking this the wrong way and being very upset, brought on by their other difficulties. Being a teenager is hard enough in itself; being a teenager in a vulnerable position is even harder.
So based on my experience of my DD's friend and working with vulnerable teenagers I admit I am looking at this in a different way to other people.
Maybe this girl and her mother are overreacting but there might be a genuine reason why this girl has taken this to heart and upset by it more than other people may be. Who knows what's going on in her life right now? Her and her mother do know what it is (if anything) so I don't think I'm going to be too harsh on them. They may well have a valid reason for taking it further.