Well, if she's falling down, the ground (the actual ground, not in the artistic sense) should be either "dark" or "medium" in value overall. From there you can refer to the image I posted above. Basically, I'd recommend some fairly extensive repainting until the values of the figure separate convincingly from the background.
The main problem right now is that you have photographic images combined with your painted fairy and background, so it gives it a cut and paste look. It's in your best interest to do a paintover at the least so that everything is the same style.
I can't see a definitive light source, the shading seems to be every where so I would try and get a sense of where the light is coming from. Some type of basic environment would help a lot in my opinion. Try throwing in some plant stalks in three point perspective and some foliage here and there since the berries make it look like she's falling from a berry plant of some sort. I would probably use some less vivid greens.
I think I will need to repaint, though, should I just drop the berries altogether? Or would that leave it too plain and boring? Trying to work out some basic compositional elements as well as some light and colour issues...any thots?
The berries seem pretty random and don't really add anything to the composition besides, as you said, being something to occupy the negative space. It certainly wouldn't be a loss if you were to remove them.
Is there any sort of story behind this? If so it might help to give us a better idea of what could be added to the image.
In my opinion, the figure/ground relationship in your revised versions is still a bit dicey. The figure and ground need to be separate from each other, and they also should each be coherently keyed so it doesn't get confusing.
Basically, the issue here is that right now the figure contains the full range of values and colors--which will make it merge into whatever background you end up using (unless you use white, as shown below.) You need to pick a color and value range (this is called "keying") for the figure and background so they stay separate. An incredibly crude Photoshop version is attached below. I hope that is of some help.
I would work on the anatomy, her arms are different lengths and her body is wrong. Also if she is falling you should show the reason, like slight damage to one wing or some visual clue, otherwise whats stopping her from flying back up?
Her hair looks as if she has already landed, with the bulk splayed out in the cross section of the direction she is falling. If you could adjust the hair along the falling axis to some degree, that would help. A bit more work on the foreshortening would help too.
But mostly I agree with the discussion on contrasting the values of the falling body and the background. Think of her falling into a crevasse.
The use of temperature might help also - warmer sharper colors the closer to the viewer, cooler more diffuse colors farther away. This accentuates depth.
Thanks guys, really. I'll try and give it another go soon....now just debating whether it's worth it to fix this up for a portfolio piece, or to shelf it and start over with a different idea.
Will update if I think it's fixable.