Doesnt matter how huge the clientel is for a trainer. It doesnt make them great trainers.
Western Pleasure is a tough class to get right, you will be penalized for excessive fast, excessive slow, uneven gaits, tail swishing, head bobbing, flat ears, poor transitions, and the list goes on.
It is more likely that the trainer has told your friend that her horse is consistent at the walk, jog, lope but needs work smoothing out her transitions. A horse that has a great consistent walk, jog and lope but sloppy transitions will be penalized. If that is not the case then the trainer is not a good as the number of students she/he is teaching.