Ask ten differnt people for a critique and you'll get ten different answers!
I do not think she is down hill built. IN fact, her saddle sits a bit too high in front. Either from the rise in her back toward her wither, or the saddle is too narrow and isn't sitting down in front like it should.
She has good bone, I wouldn 't say calf kneed, but close to it. Just a bit overly straight at the knee, perhaps? pasterns are a bit short and her toes , especially in back, are too long and heels too low. Farrier can make some improvements there.
She has pretty good balance overall. I think standies are bred to trot, so I dont' know why she wouldn't do well in either endurance or trails.
Even low level dressage would be fun on her.