The best person to ask about specifics on what a draft can/cannot have would be Solon, but I haven't seen her around for a while.
The only thing that I have noticed with my drafties is that they seem to eat more, tack is more expensive, a farrier is hard as hell to find and even harder to afford, and if they are pushy, then there is a big problem.
Personally I really like her even if she is skinny. I haven't been around Belgians regularly for a long time but I do know that they are the more steady, levelheaded horses of the draft breeds. Once Bessie got over her initial uncomfortableness of the harness, she settled right in and nothing fazes her now. Of course, a PPE would be in order just to ensure that the skinny is, in fact, due to lack of groceries.
But if you would rather I say this "NO, DON'T BUY HER. SHE LOOKS LIKE A KILLER FOR SURE! SHE IS TOO BIG TO EVER RIDE AND I'M SURE SHE WOULD ABSOLUTELY HATE CONSTANT ACCESS TO FEED AND PLAYMATES."