What is this book???

So a few years ago I found this book at a library. I never checked it out because I finished it in the 3 hours I was there.

It was a blue book about a girl who was jealous of her younger sister. She was prettier, smarter, and dating the older ones crush. Over the summer they are involved in a boating accident and the OS’s best friend became paralyzed and the younger sister passed away. It talks about grief and intertwined are comics that featured the characters as creatures from Greek mythology.

She is Medusa.

Please help me find this book!!