1. Expose for the subject not the background.
2. Use Manual mode on your DSLR for greater control over exposure.
3. Shoot at a low ISO to reduce noise.
4. Frame your image so that you don't have bright areas in the background that compete with dark areas in the foreground for proper exposure. In this case your camera exposed for the background leaving her too dark. This is most apparent in the other picture of her on your flickr account.
5. Be aware of what your image is trying to communicate and make sure you compose your image to best articulate your vision. Your subject is located in the center of your image, which is fine but is best suited for symmetrical poses since your empty space on either side of the subject help reinforce the idea of symmetry. In your picture she's looking off to one direction so centering her conflicts with the direction she is facing. Try positioning her to the left as she looks off to the right. This suggested composition invites the empty right part of the photo to become part of the image instead of serving no purpose.
1. Because she wasn't well exposed to begin with, you found a lot of noise when you tried to brighten her up. This lead to using too much noise reduction which causes the image to look blurry. Try and use a sharpening feature like unsharp mask in PS to sharpen important features like mouth, eyes, clothes, etc.
2. Use Masks to control which areas of the photo you brighten. Her dress appears too bright and therefore you've lost most of the detail in her white dress.
3. I appreciate the sparkle effect on the horn. When doing special effect in editing you need to understand how light works. Light almost NEVER has a sharp, hard edge. So try using a soft brush to apply the color, so the blue color gradually reduces at the edges.
4. A fill effect would do wonders on revealing some of the detail in her hair. Adobe Camera Raw or Lightroom have this feature.
5. In post you can change composition to make your picture more dynamic. I went ahead and cropped this image ONLY to demonstrate what I was talking about earlier, so you can visualize it. I won't post it here because I think that would be disrespectful without permission, but i'll send you a link in Private Message so you can look at it.
Compared to the other image on your flickr account, I think you did a pretty good job in creating/salvaging a good image. It is certainly usable for social media and the like. As you play with post processing more and more, you're skills will grow stronger, so just keep at it. Understand, none of what I said is a MUST DO. They are just suggestions and tips you can use if you find yourself having trouble with how your images turn out.
I think you've already discovered that shooting the picture correctly is the most important step. Post Processing can only do so much and is limited to what comes out of the camera. So make sure you are aware of your lighting, exposure, and noise while shooting. Also just a tip, if I'm uncertain on how bright I want my subject exposed, I prefer to shoot a little darker as opposed to shooting it too bright. In my opinion, it is easier to salvage a picture that is too dark than it is to salvage a picture that is too bright.
Hope this gives you some ideas.