I never phrased it as “problem solving,” but there were a couple of horses I’ve encountered who seemed to act as if every day was a new day. Spook at the muck bucket that’s always in the aisle. Spook at the winter sun that reliably shines on the sand on the indoor every winter afternoon. Get them through a puddle one day, finally, successfully. The next day, same reaction at the puddle or the pole.
In one instance, the horse was a camp horse and arguably being handled by inexperienced kids can reinforce that behavior because they don’t have an experienced person’s confidence. On the other hand, it’s exasperating that you have to lead a pony thinking UNSTOPPABLE CONFIDENCE-CHARGE every time you literally go over an objectionably white pole on the ground.
Another horse (circling back to what someone else said) was a dressage horse who was pretty talented, and by carefully managing his environment with confidence and predictability, he had success. But I think that is easier in dressage than jumping sports, or, obviously, trail.
This is gonna be one of those whacko COTH forum questions but…are her eyes okay? Sometimes vision problems can make the world look scary and lead to a lack of confidence.