I spent a good portion of my life re-schooling Widowmakers and by that I mean horses so "out there", even the 6' tall, football playing, trail riding guys I grew up with, wouldn't go near them.
If you're going to get serious about this school project, it's not as simple as "theory" and what "seems/sounds" like the right thing to do. Each horse is different, just like humans are different and will react differently to the same source of abuse.
Honestly without the experience to speak first hand on the subject, the project might be better switched to title "how to nutritionally rehab an abused/neglected/abandoned horse. It's a given the bulk of abused horses are also not being fed properly. If the owner doesn't care about beating them half to death, they sure don't care about feeding them.
I never did anything with a horse when I brought it home except turn it out to pasture with my Keeper horses, just as soon as the vet said I could.
The pasture and my horses were its safe haven and my horses were the first "therapists". It learned the feeding rules first and foremost.
The horse always told ME when it was ready for something extra. If hooves were in bad shape, I did start working with the legs/hooves right away so neither myself nor the farrier got kicked in the head.
Never push an abused/neglected horse - that delays trust. Saddle? worrying about saddling the horse was the last thing on my list. I was not under a timeline to hurry and get things done. The horse made progress mostly on his terms; the exception would be if I sensed the horse wanted to do a task but wasn't quite sure.
That segways into "having a sense" for what the horse is ready to do next. Without that Sixth sense, the person attempting to re-school an abused horse might just as well hang it up, for the most part. Granted there will be things that will stump the human but they should be the exception, not the rule.
Bottom line is, don't attempt to rehab a horse unless one has a lot of experience working with horses --- brushing, picking hooves, saddling to ride excluded. It's not a black and white "I am going to do THIS and you should respond, in kind, because it makes sense to me".
Horses are not machines, they're 1000 - 2000 pounds of possible danger if the human can't look six plays ahead in the re-schooling Game of Chess