Chelsea Manning has my full support in this particular regard. Even if one disagrees with her tactics, one can still support her transition and desire to be identified as female. However, I suspect she will find it difficult to transition in a military prison. They don't cover hormone therapy and SRS. Likely, this will end up in a lawsuit. To be honest, I doubt she will win. Perhaps in public opinion, but not in the courts. Nevertheless, I hope I am wrong as I don't feel anyone should be denied treatment for Gender Dysphoria.
On a side note, I was talking to somebody close to me about "Bradley" Manning today and asked if they heard that she came out as Chelsea. The reply I received was "is that the football player". Turns out this person never heard about "Bradley" Manning, Wikileaks, or Julian Assange. I found this to be more shocking then Chelsea's coming out and plans to transition,lol.