I have never seen a horse with actual saddle marks that look like that. I guess anything is possible, but I think the saddle marks are just dust. She was probably just ridden and put away. I say that because I used to have a horse the same color and when he had his winter coat anytime you touched him the dust would come up from his coat. If you patted him you would leave hand prints.
If she is sound and you just want a pleasure horse, check her out. She might be good for more, but if you are only going in with the goal of her being a pleasure horse then you are less likely to be disappointed if she doesn't have the athletic potential for more.
She certainly deserves a chance with someone who will care about her.