@DrBlackbird
A book being selected for GCSE has no relation to its age appropriateness.
A Christmas Carol is regularly taught in Year 7 - in fact, according to recent research by End Sexism in Schools, it’s one of the most popular texts taught at that age group. The same with Of Mice and Men.
At the same time, A Christmas Carol is the most popular set text at GCSE. Of Mice and Men used to be before Gove took all non British literature off the list.
GCSE Literature is being increasingly dumbed down with its text choices to reflect the fact that in many schools now it’s compulsory and there are a large proportion of young people for whom English Literature is a huge struggle. Being able to teach a text designed for much younger readers - i.e. Coram Boy - gives those students who struggle a better chance of being able to pass, because the content and language are not as challenging.
Coram Boy is generally appropriate for children aged 11+ but as with all forms of media, it is not for everyone at that age. It does have some distressing content, but handled sensitively and alongside a teaching of the historical context to ensure children understand this is not something that could happen now, it can be taught well and enjoyably to a Year 7 class.
Literature as a medium allows us to explore a whole range of experiences outside of our own. In a class there will always be children for whom some of those experiences discussed in a text will hit home more than others or trigger upsetting memories or so on. We can’t avoid children having to deal with feelings and emotions when they read. It’s about knowing your class and working with them to help them contextualise and manage their emotional response to fictional events in a healthy and productive way. If we never expose children to things they find upsetting or hard to cope with, they will never build resilience.
That being said, if the OP is genuine, I would imagine her rather highly strung approach to life has rubbed off on her daughter, which will have contributed to her response to Coram Boy.