Found: YA mystery/thriller

I've been looking for this book since I was 13 (ten years ago) when my library suddenly discarded it.I remember it seeming a little older when I read it, so it was probably published in the late 90s or early 2000s, and I also remember it having a blue cover. The plot revolved around a teen girl recovering from some sort of accident at a hospital/psychiatric ward, centring mostly around letters to her younger sister. A plot point of the book was that the sister ended up not being real or having died years ago. What stuck with me was a scene in the novel in which the protagonist, in a flashback, recalls having her head slammed into a car door/dashboard by their abusive father and her ear bursting and filling with liquid. For some reason that scene really impacted me and I'd love to reread the book.

Me and Emma by Elizabeth Flock? I'm not sure all the details match because it's been awhile since I read it. If it's not the right book there are similarities for sure.

Wow, I completely forgot about this post for three years apparently, but yes! That is the book! Thank you so much!

You're welcome! I'm happy to have helped!