Without a video of her movement it would be impossible to speculate on her future as an upper level dressage horse. Getting only a 56 in an Intro test might indicate poor movement, but also it could mean a rider that couldn't get what is needed for a better score. IMHO.
Juno and I got a 50 in Training Level 4, not b/c she was unsuited to dressage--a Dutch clinician said that she could easily reach the Grand Prix level--but b/c I was just sitting on her, not riding her. I had no idea how to RIDE a dressage test then.