Well, I can understand that sentiment. What I meant about prayer works was I prayed for you to get an earlier appointment, and YOU DID!
Humans have been discussing how God works since the beginning. For me, it's simple. God created us for a relationship with him. The original fall/sin separated us from him and brought down the perfect world he had created for humans.
Then he gave us a way back to that relationship with him. He doesn't make us sick, evil/our fallen condition does, but He can heal us.
Why doesn't He heal all of us, I don't know. Why he hasn't healed my wife, I don't know, but I do know I have prayed fervently daily since day one and believe He has given me insight and wisdom to help her condition slow. In the relationship with him, our life is not about the condition of our life, but about the condition of our death.
I'll keep praying for you and your sister.