Book, video, YouTube and knowledgable horse persons are all excellent resources. One important resource is lacking, however. None of them can convey the sense of FEEL. Feeling the rein in your hand, is the horse even on the rein from both sides – is the RIDER? Can the rider FEEL a possible hump in the back which could spell trouble – and then feel their response to avoid that trouble. Can one feel the confidence and convey to the horse, when one hasn’t experienced the feel of a horse in need of it?
Horses are tactile creatures.
Also, the horse who has been born and grown up in herd situation is not going to be happy when separated from them – and particularly when trailering for a first time, as has been mentioned.
The situation as written does not bode well. Better a “made horse” for this.