My 8 year old daughter was diagnosis rsd. how accurate is this diagnosis?

Rare in kids: I think you're referring to "reflex sympathetic dystrophy", which is quite rare in children. It's more commonly called "complex regional pain syndrome". There is no single test that establishes the diagnosis. If this is being considered in an 8 year old, you should probably be working with an interdisciplinary team including pain specialists, neurologists, and pediatric mental health specialists.