The farrier should understand the inside of the hoof. Not just by holding a vertically cut-in-half, 2-D model and pointing at half-bones.
Farriers and trimmers must attended an equine foot and leg anatomy course, in person, to understand what they're dealing with. You, as your horse's friend, might consider attending one as well.
The hoof consists of bone encased in a huge vascular system, tendons, ligaments, digital cushion, cartilage, and of course, the hoof wall that protects this living, dynamic interior.
Domestication has replaced an environment that shapes a natural equine hoof, such as tough steppe and rocky grassland, with stalls and "bedding," and "runs," and lush, wet pastures. Therefore the job of your farrier/trimmer is to help the horse maintain his foundation, his connection with the ground.
The hooves are your horse's other four hearts, pressing with every step to pump blood back to the relatively small heart in her chest, the other four hearts that you can literally feel as you walk beside your friend.