Cordana was newly introduced in WoD, so we don't know too much about her.
She has been there from the beginning, did a good job at protecting Khadgar and appeared very loyal so far.
She grew kinda annoyed with him using the tools of Gul'dan and generally his "mooooar Powerrr!!!" acting.
After Khad freed Garona from Gul'dan, she claims the orb of dominion and says she will destroy it.
What would happen if she did not destroy it? What it she - a little like Maived - turned from good warden to crazy warden. What if she feels she has to "stop" Khadgar and for that starts working with Gul'dan?
Maybe just in the moment we stole Garona from Gul'dan, maybe he stole Cordana from us?
Might be a far shot, yet until now people have been more busy with Khadgar's worrying lust for power. Might be Blizz is leading us on a wrong path...
What are your thoughts?