Interesting idea, but rather careless execution. I would put more emphasis on hands, perhaps shooting from above and filling the frame with just hands, also adding contrast and doing something with that glare in the middle of the frame.
Excellent idea and B & W works terrically for me. Wish her elbow was not cut off. Also lead in of the instrument might work better if coming in from the corner....
I was thinking it would be the vibration of the strings. Always useful to have and extra pair of hands even if they're shadowy. Nice capture of the movements.