She's got a long neck that does not tie in well at all but he should clean her up there. Her topline is a little weak (depending on how many babies she has produced) but he does have a nice short back and good round croup.
So that gives the foal the best chance at coming out being a better athelete then either parent. For a prospect that's not a bad price if she has produced nice foals before (keeping in mind the stallion she was bred too). They say she is proven so I'm assuming she has offspring showing because I don't think just because a mare can mame a baby she is proven (check out the human race for a prime example) so I'd ask for more details.