Ballerina at rest - two poses

My regular fortnightly life-drawing session had a new twist this time. Our model was a ballerina wearing a leotard and long lacey ballet skirt.
After a few quick practice sketches, we did this pose of 20 minutes, with our model curled up as if resting or sleeping. From my angle, this proved quite challenging with the legs mostly hidden from view. I chose to use Conte crayons on a coloured paper, in order to capture the white of the leotard and the skirt.

We then did a longer pose of 55 minutes, which I found quite inspiring and rather reminiscent of some of Degas' pictures, where he captured the dancers in off-guarded moments.
I have tried to depict the tranquility of the pose as well as the delicate muscularity of the dancer herself (such as the prominent collar-bones). I have to admit the face is not a good likeness of the model and I'm not sure about the left arm and especially the hand tying the shoe-ribbon.
But on balance, I'm not too displeased with the overall image.