I would be a bit annoyed at a gifted program me that aimed for a diverse group in the top 15℅ rather than serving those that truly need it. However it is what it is. You can't really plan because you don't know what they are looking for. Well rested, fed and relaxed is as good as you can hope for. Maybe do something interesting a few days before so she has something exciting to talk about if asked what she enjoys etc.