My sister was ten back in 1952 when she became ill. She was in the hospital for 30 days, but they couldn't figure out what it was. When she was 15 they discovered her heart was affected and finally figured out it was rheumatic fever brought on by a strep infection. Her mitral valve had to be replaced eight (8) times, starting when she was 18. She is in the medical records. She married and had two children who are now 49 and 47.
Your daughter will be in my prayers. I know it's tough, but God will see you through.