Yo, I really like that 10 min study, I feel you definitely got her likeness in the face and I like how you used some overlap in the silhouette of the arm to denote the biceps brachii and the skin folds at her back. Also the proportions look good
I know this was just a 10min sketch, and presentation at this point might not matter when you are just suggesting the shading, but it does look a little messy when the lines you use to describe it are chaotic. In stead, try using lines that go parallel to each other (crosshatching), these can be straight in any direction within the boundaries of a shape to just to give an idea of a shadow or they can be curved and follow contour lines suggesting the volumes and shading of an object. Make sure to lift the pencil/stylus/pen off the canvas for each mark made and it will look much cleaner
Cheers and keep it up!