Very nice!
I dig the muted palette and the galaxy hair is a good idea. Also, nice job on the fabric.
A few small things I noticed.
The light shapes above her hands are symmetrical. Which isn't necessarily a bad thing - if there was something in the image to give it purpose, say the light rays they are giving off converge to a focal point then it would make a lot of sense. I think in this case though it looks like you may have used the symmetry tool or just copy/pasted the same one. A few small variations in them would solve that.
The moon at the top of the image draws a lot of attention. It might make sense to have it perfectly circular. You might need to use the circle tool for this, even if just for a guide on a different layer.
That's just my 2 cents. Overall I love it - keep up the great work!