Mathilda and Ruth, aka Tilly and Roo. Two sisters, so excited to be in the same school again once Tilly entered ninth grade. They understand each other and tell each other almost everything. They share their lives, they commiserate about their parental units, they gripe and complain to each other. One does not fully exist without the other.

Then a dog runs in front of Roo's vehicle as she is traveling to pick up Tilly. The ensuing crash devastates her life.

Locked in syndrome.

Ruth Ann is now fully paralyzed except for vertical eye movements. However, she is perfectly conscious and sentient; she can hear and see what is going on around her. Luckily, one of the doctors is able to accurately diagnose her and set up a computer to help her communicate. Roo can now speak in full sentences, and the computer decodes her thoughts.

Roo's world consists of staving off despair; her salvation comes in the form of her doctors, her mother, her sister, and friends.

The Secret Language of Sisters by Luanne Rice, 2016

I am always a sucker for sister books.

Luanne Rice's web site

Books on locked in syndrome