Nice! This is a lovely painting.
I have possibly a few suggestions to give you and to make them clearer I did a quick-ish paintover, so I hope you mind.
First I wanted to check the character's anatomy just to make sure everything was okay.
The only thing I really found was that the placement of her left arm made it so she looked she didn't really have a neck, so I moved it.
And then here's the rough paintover I did.
The first thing I noticed is that you used a lot of whites or bright near white color to shade the highlight. You usually want to keep those for the light sources, very reflective surfaces or small highlights. Normally lighted object don't go as bright as a light source. I also tried to define the hair a bit better as in your illustration the hair come across a little bit as being of a similar material than her dress.
Then, since she is in overall blue environment, I added blues to her skin to tone it down a little, especially in the shadows. In that same vein, I darkened the left side of the picture using a darker blue and brought back some of the highlights to really allow for the magical glow effect to shine and add more ambience. Then I did the same on the right side using a bright yellow to add a soft glow of light.
Lastly, I thought that the environment was a little too ambiguous, so I added the suggestion of some archways in the back and added some details on the platform she's standing on just to add a bit more context to the scene. If you want to do something like that feel free to add whatever you want, those are just what popped into my mind while I did it.
I hope this was helpful and that it didn't come across as harsh or anything. Remember that a lot of those are just suggestions that you can try, so feel free to take what you want and ignore the rest.
Keep on painting!