I think you already knew before you posted, but it's not really that it's too dark, it's that too much of her blends with the background and has lost separation. Perhaps if you have the raw file you could open the whole thing up somewhat and get some of that separation, possibly open her face even a bit more and then burn down the whole bottom and lower left to minimize the distraction of the surface she's laying on.
It's not a bad shot of her by any mean. You've posed her well. She's got a good attitude turning her head toward the light and eyes to the camera, but it just needs some massaging. You could probably crop it considerably and that would help it as well.
+1 on the crop. I also agree on darkening the surface she’s on. The eye usually goes to the brightest part of an image first. That surface is slightly brighter than her face and competes for the viewer’s attention.
Some great suggestions, but it's a great shot as it is, so don't get too carried away with the modifications. She is a very beautiful woman and you posed her well. Shadows are a feature that adds depth to photos if controlled well. You are almost there.
As others have said and:
- I'm not that bothered by the body lacking separation, I don't think it's a bad thing.
- I am bothered by broad lighting. The subject's face is somewhat square, and might have benefited from short lighting.
