I'm so intrigued by what you said at the top about using fanfiction in mental health treatment. I've definitely talked about fanfiction in therapy more than once. Is there someplace I can read more about that, or any more you want to say about it? (I get if you don't want your thesis on the Internet or have other worries about saying more, just figured I'd ask since it sounds great!)
There are whole academic journals dedicated to fandom if you have access to a university library. I could also talk about this forever. Read up on Narrative Therapy and that'll be a good primer. The main idea is that we can use fiction to re-parent ourselves. Trauma is not having the resources (by no fault of our own, you can't prepare for trauma) to face whatever horror came our way. We often didn't get the guardian we needed, but we can write and read that guardian as a way to re-parent our wounded inner child. If you're not able to give yourself credit for what you survived, that's okay, but what would Hermione have to say? Molly? McGonagall? Can you feel righteous anger though McGonagall or Harry? It's all you, it's all your own wisdom, the character is just the mouthpiece. Trauma also leaves us with so much anger and depression that feels inappropriate in life, and the events in fiction are so big and dramatic (ie dark fic) that those emotions now feel like appropriate reactions, and we can explore our depths of emotion in a safe, contained space. So it lets us come at the trauma sideways, which makes it accessible, see it through a new lens, and rewrite the story.
Also, trauma doesn't have to be TRAUMA. Growing up in a capitalist, racist, white supremacist, fatphobic, ableist, cisheteronormative society IS traumatic. None of us escape that shit. We all have wounds to heal from it.