That's a nice sketch. I like the posture and setting but I think there can be some improvements as a line drawing.
The waist of the lady has too hard lines. Then the baselines for her head can be seen and it appears that the knot (middle of the back) is tied a bit too close to the back of her head. Push it outwards slightly. Her left shoulder and neck also appears to be too rounded or bulged out.
The zither is undetailed and mishapen compared to the lady, possibly because of the lack of any height there (due to lack of shading), it looks flat. Also I feel the strings could be done fainter but really straight (to reflect the tautness)
The edges of the room she's in is misaligned with the carpet. Have them parallel. The support is leaning towards her. It looks like the building might collapse on her :P. I think it might be better to change it to a round pillar instead. If you could go for complexity, the pillar would have a coiling dragon design on it.
Well, I get the feeling that this is actually a rough draft and all I've said has already been noticed by you. Judging from parts of the Wicked Nymph and Miyabi Ningyo, I'm certain the finished product will be different from this. I look forward to seeing the final product :)