This art is absolutely beautiful.
I'm no artist, so I can't go into analyses of your use of colour or composition (other than it's exemplary), but I will say this: This is one of the best pieces of Halo fanart I have ever seen. In fact, one of the best pieces of art I've ever seen full stop.
You've absolutely captured Cortana here. Most of the Halo fanart so rarely does her justice.
(I've just fulfilled your bet, haven't I? sorry, I couldn't help myself).