Hi there. I just wanted to say, this horse sounds like the kind of horse who has been feeling quite 'alone' and in bonding with your daughter has formed that special type of friendship that you sometimes get just once during your lifetime with a horse. They have built that friendship up in their own unique way of communication and it is on that the trust was built, and the horse has learned to respond to her.
The trainer you brought in seems like an aggressive 3rd party who does not understand that there is a difference in horse personality types. No one horse is exactly like another and there are these rare horses that are extremely effectionate, if not dependant on their owner. By handling him like they did (the trainer) they have wedged themselves inbetween the bond formed between your horse and daughter.
I think its very good to have a trainer/instructor, of course! But -if- that trainer starts to come inbetween the rider and the horse to such a degree that there is a distinct shy in the horses behavior from how he was before -fear- turning away from one he trusted, ect, its bad not only for the horse, but the rider, since it means the trainer is not recognizing the situation for one that has become bad.