Wait, Revek could replace an ENTIRE BRAIN, but not a heart?!
Like, the heart is not exactly a very complicated thing. It's a muscle working in a rather complex way, but nothing that couldn't be solved by machinery.
But the brain? The most complex organ in the entire human body?
My only guess is that they stuffed one of the Brackern-stones into her and the soul of the Brackern merged with Orianna's mind to create something new while powering the machinery... would at least explain how she could move the sphere, if for the soul-stone it is seen as part of her body.