It sounds as if you have a horse who is young and he is large. The fact that he is big may be intimidating so make sure whomever is working with him has the confidence to do so. By the horse breaking free and going out of control with first trainers attempts, you can bet he will repeat the behavior in the future. Unfortunately bad behavior that is left unchecked will only escalate and become habitual. In a horses head, if it works, they will do it again. You really shouldn't have such a fuss if you have laid a solid foundation. The behavior displayed by this horse says he was being asked too much, too soon. I would start from absolute ground zero with a very consistent routine. That means make a commitment to work with this horse daily, you have to desensitize him to work & he needs to be placed back into the "submissive" or "follower" position. This will take a very strong confident individual who knows what they are doing and is not intimidated by his past outburst nor his size. If your daughter is just starting out, I would say you should find a trainer to do this. I wouldn't even bother putting her on the horse with the lunge. He sounds like he is really green. I have had issues with horses who are fine with a walk and a trot, but when asked to enter a gallop, they do feel a little "frisky". My horse is so docile I have let 5 year olds ride her BUT even now after much work, sometimes when we hit a gallop, she will shake her head and give a buck or two, she gets frisky on me. I just ride her through it. A word of warning though, if you feel at all like your daughter is outclassed by this particular horse, do not feel bad about selling it and getting her one that she will be able to enjoy safely without these "frightening" episodes. If this horse is not handled correctly because he is just starting out, his development and training will be flawed. I would find a trainer to finish him out so he learns all the right stuff the first time around. Remember most of the horse training we do is not in the round pen, it is in every interaction we have with our horses. They are always learning something from us, be it bad or good. Certain things should be left to certain people, and I say that in the nicest way.