Ok, so I think I know why it looks so superimposed. I did a really rough edit to give you an idea where I would start from.
First - because of the pure white back ground, the the exposure of Zoe is too dark, she needs more pop. I selected her and adjusted the Exposure, Offset, and Gamma Correction untill I got where I thought she should be. I then went in and toned down the Magentas because they had blown out into her shirt. I then did a little Dodge on her eyes, because the whites were still too dark, some Dodge on the teeth because they looked really yellow, heal brush on her forehead to take that spot out, and then tuned down the yellows, as there was an unnatural yellow hue to her skin tone.
The whole area around her where you cut her out needs to be softened/blurred. There are a lot of jagged lines following where you cut her out. Zoom into her at are 200% and follow her outline and you will see what I mean. I think I would just use a stronger blur brush and smooth it out. It follows into the curls in her hair where the background is cut out as well, so where you see white and her outline it will need to be done. I didn't spend a lot of time on that, simply because it could take awhile.
After all that I did a little noise reduction, High Pass Sharpen, and Unsharp Mask. And I think it turned out ok, but it's still rough and could use more fine tuning. I hope it helps, maybe it will give you some ideas. Good Luck!
