Is she going to be made out of different kinds of rock? Fantastic idea! I'd love to see you in some of your color comps, make her look like she's made out of some kind of gem :)
I did some drawing on this to try and refine the features to see if I could make it more appealing. I would try to maintain a good silhouette and try to let the rock forms follow the form of the figure more closely if possible, then plan on using textures to indicate the rock creases when you model the character. Then, toward the end when your'e happy with the textures applied onto the model, you can carve some slight clefts into the geometry to get the sense of the figure being made of rock. I hope that makes sense. I will try to explain it better next week in class.