What is the CTY process and what are the advantages of testing for it? It gives you access to online learning, I think, but anything else?

I am reevaluating DD right now and feeling a little flummoxed. It is apparent from conversations with her teacher and what I am seeing from school that the gifted magnet may not be adequate either. It does look like this is a better fit than her previous school, and I think she is going to have more friends here. But we may need more.