Like other have said, high withers isn't poor conformation, although you will have to be careful with saddle fit. It's certainly possible to fit a saddle to a horse with high withers though. I had a great hunter with major shark fin withers and she was (and continues to be) successful at A/AA shows, so it's not like it was impossible to find a saddle that was comfortable for her.
What would you want to do with this horse? For a sport horse, there's really no such things as too uphill - it's a downhill build that will limit performance in jumpers/dressage/etc. It looks like this mare is standing on a slight incline, but there are still a lot of things I like about her build for a sport horse. And some that are less common in a TB! I like her open shoulder angle, and the placement of her front legs. She has a nice length of pastern and good bone for a TB. Her legs look clean in that photo. I love the depth of her stifle and her LS placement and short loin.
She looks a little unthrifty, and I'd prefer to see her with more weight. I think with good nutrition and proper work she'll develop that topline a little more and make the withers a little less notice-able.