Can you get more/better pictures? I think it might be good to take your trainer with you to look at a horse. It's very difficult to tell much of anything with these pictures.
The back doesn't look sway back to me. The neck looks quite thick. Is this horse post legged? If you want this horse for rodeo work I'd want to make sure it is not post legged. How much are they asking for this horse?
It's kind of hard to tell with the pictures small and at an angle. Very pretty. I don't see the sway back they are talking about, and as for the thick neck, it's hard to tell with her coloring if it actually is or not. A spot of color here or there can make a horse's conformation look kind of funky.