Tom,
It sounds awful that your daughter, you and the rest of your family have to go through this. As the others mentioned, she has her youth on her side. Children have the greatest chance of remission. The Chopra video is quite informative, so I would give my recommendation on that as well.
There are cases of CRPS showing up without a preceding event. I can not say for certain if this is the case with your daughter but it can not be ruled out. There could have been additional trauma that went unnoticed at the time of her concussion last February. I am sure that the knee surgery did not help as surgery has CRPS to increase in intensity following further traumatic events that includes surgery.
We are here for you if you should need someone to talk to. We are a friendly group and are more than happy to offer our advice, thoughts, knowledge, and most of all, support for each other.
Healing thoughts and hugs for you and your daughter