Musical cats

This is a world where, after death, people become musical notes and enter the beyond, where they live happily and without worries. According to legend, when pianists on earth play different melodies, the notes enter the beyond, and cats eat them.
This is a story about a girl pianist and her little sister. The girl's name is Sofia, and her sister's name was Sasha... until one day, Sasha was hit by a car. She was calmly playing on the playground with friends, and her friends suddenly suggested they go to the store across the street. Sasha was afraid of cars, but afraid of losing her credibility with her friends, she agreed. They walked hand in hand across the street, but Sasha became scared and fell behind her friends. The traffic light started flashing. Sasha stood frozen with fear and couldn't move. She was hit by a car. The grief-stricken sister began playing the piano to at least somehow channel her grief. That was four years ago. Sofia is now fourteen years old, and she still plays the piano. Her father is rarely involved in her life and has long since fallen out of love with her mother. He hasn't left only because he doesn't want to break up the family and further torment his daughter with grief.
Sasha is happy in heaven, and she's always the first to run to the notes emanating from her sister's piano. In their world, everything is wonderful and carefree. There's always wonderful music playing, and the cats are safe. The sun is brighter there, and the grass is greener.