Wow. Just, Wow.
Mia would have been an interesting girl to get to know even in a less eventful book.
Just her story as a classical musician in a family of rockers alone would have been worth reading.
Just the story where she was a teen in a family where both parents loved her and she loved them, and they could talk about some (although not all) of the relatively normal teenage things she experiences, that story could be a good one.
Just the story of her best friend and her boyfriend and how they all learn to respect each other and their relationships. That might be enough.
But all that is the background. The real story is after a car crash, it is what Mia is thinking, as she’s reflecting on her life, on her possible death, and trying to decide what will happen if she stays.