You had a lot of critique so i'm just going to go on the assumption that none of what I am about to type has been pointed out (don't have enough time currently to read through them all). Anyway; I would really consider using softshading over cel shading. For two reasons. One: you must understand that before you can accurately cel shade efficiently. Two: a lot of the details are lost and become a bit... well, confusing to put it kindly. Take the mouth for instance. I assume they are supposed to be lips, but because it's a single block of colour all I can conclude is that she either wears lots of lipstick, or has no teeth.
The neck is oddly consturucted. Generally a neck would the a slightly curved cylinder (to imitate the cervical region of the spine), and then with that you can apply muscles such as Sternocleidomastoid and the Trapezius. However your neck appears to taper outwards as it is joining to the body. Now I believe this was your attempt at introducing the trapezius to the neck, however to avoid this issue, I find it is easier to first of all draw the cylinder for the neck, then the shoulders, adding the trapezius last so you can avoid it looking incorrect. Here is a doodle I did in case I don't make any sense O_o
EDIT: Also since her left arm is being raised by the rotator cuff (muscles associated with movement of the upper arm), many of them will be bundling together to pull the shoulder girdle upwards. I think you would see the "double hill" shape slightly as the deltoid and trapezius pull together to raise the arm up. Here is a more exaggerated and poorly drawn version of what I mean;
In the context of the pose;