I have to say, I quite like the black line of the thong. It's not traditional figure study form, but the tattoo isn't either, nor is the pose.
While I quite like the picture, there are two things I think are worth thinking about:
where is your focus? It seems to be on her elbow in this one, which I don't think is a very strong choice.
where is the viewer supposed to look? The line of the thong and arms suggests that we're supposed to be interested in her coccyx, which isn't a bad choice per se. The focus conflicts with that idea, as do other elements. The point of highest contrast is more or less her tattoo where it is crossed by the thong, the tattoo is inherently interesting, and so on.
So you have focus, leading lines, and contrast/light all pointing us in different directions. I'm not a fanatic about leading lines, or any other individual thing, but getting more alignment between the elements would make this a stronger picture.
Just a specific suggestion, then: move the camera down and to the right, to hide her coccyx, and that interesting joint in the thong that leads the eye. Focus on the tattoo. Burn and dodge to emphasize the contrast in that area, and de-emphasize it elsewhere. Use the thong strap as a diagonaly element across the frame, to add dynamism, but try to eliminate it as a leading line that goes somewhere not-interesting.