Elsewhere by Gabrielle Zevin is about Liz Hall, a teenage girl who dies in a hit-and-run accident and wakes up in a place called Elsewhere, which is the afterlife.
In Elsewhere, people live their lives in reverse: they arrive as elderly, grow younger, and eventually become babies again before returning to Earth. Liz struggles to accept her early death because she feels she never truly got to live.
Over time, she adjusts to her new reality, forms new relationships, and slowly learns to accept death and find meaning in her afterlife.