Some pictures from the side and straight from the front would be helpful. I can’t really tell you anything from the angle you have. Splints are typically just blemishes but if she becomes lame you should have them looked at as they can occasionally rub the suspensory ligaments. It would be best to bring her along slowly for now. 18h (wow!) is a big girl and that’s a lot of force coming down on those front legs when she lands. If she’s over at the knee very much she will be prone to injury. Her conformation is pretty set at this point in her life and it’s unlikely she’ll grow out of anything, though she may get a tiny bit taller still and developing some muscle will be good for her. Corrective shoeing may help with the pigeon toe. Keep in mind that her extra large size may interfere with her ability to shorten her stride in some of the tighter spaces seen at prelim, a 9 foot bounce might be tough for her. Good luck!