Hi there,
First of all, that's a really great image. And it's very clean. I like it.
As for some C&C, I'll start with the raised hand:
Something about it seems a little odd, and it's hard to pick, but I think that it is the placement of the wrist joint - it seems too flat. I think it needs to angle outward just a little, either that, or bend the elbow more and bring the hand closer to the head. It's minor, but I'm being thorough.
The collarbone, in my opinion, is too defined for such a young girl. You could get away with removing the small dots at the bottom, and maybe even the tails on the lines (those that curve downward). Though I'd leave a small part of the curve there.
I really think you've done a good job of the shirt and the pleated skirt. Only one thing I would do is add another line to the shirt. I've tried to add a picture in, but i don't know how successful I've been with it.
Now, the feet. I know that the front foot needs some work, but the rear foot is pretty good. It *might* benefit from a small shadow of a bulbous curve for the heel, but it's fairly good as it is. But the other foot needs a little more. It's not, by any means, horrific, don't get me wrong.
Because the rear foot is angled inward, and the girl is running forward, the other foot should also be angled inward. Another point would be to also have her running on the ball of her foot (ie: round the toes, put a bit of a flattened ball down).
I hope I've helped.
Good luck