Hier das hab ich gefunden( Ist aber auf Englisch) Ich hoffe es hilft :) :
Biography
Background
When Kaori was 5, her class went to see a music recital, there, she first saw Kousei. His playing was magical and at that moment, Kaori decided that she would be a violinist and have Kousei play with her. Kaori was always a weak child, and underwent many surgeries. She wore glasses, and didn't eat very much to appear skinny.
One day, she saw her parents crying in the hospital as they realized she didn't have a lot of time left. Because of this, she decided to live a full and happy life before passing away. She put on the contacts which she never had the courage to wear, ate a lot and ignored the aspect of her appearance and played the music the way she wanted to and not how everyone else wanted her to. Then, she told a lie.
Shigatsu wa Kimi no Uso
Kaori's parents own a bakery shop that further develops her happy go lucky, free spirited personality. It is often shown that Kaori loves children and was often seen interacting with kids about music. Kaori also appears to be hiding some type of illness[1] when she collapses during her first performance with Kousei. While she only claims to be anaemic, there are hints of deeper health concern with Kaori as she's seen with a large pile of medication during Kousei's competition and was also unable to participate in her callback round with Kousei due to being hospitalized. Since she wasn't able to perform with Kousei, it is later found out that she was bleeding and had to go to the hospital. After this incident Kousei went to check on her since he just found out about her in the hospital.
As Kaori's final days were coming, she wrote a farewell letter to Kousei. On February 18, the day of Kousei's piano competition, Kaori had her operation. At her funeral, her mother gave the letter she wrote to Kousei.