Weight is fine. It's her lack of heart-room which makes her look elongated and slim. Having a low set on tail from a slight goose-rump doesn't help (unless it's the angle she is standing at). I am perfectly happy to see a pony in her body condition, and her coat appears to be in good order with a shine on one pic. You could improve her neck with correct work but don't be tempted to put extra weight on that frame - she'll just get tubular (and laminitis). Is she a New Forest?