Seeing such threads is always aggravating for me, as I would rather live in a world where no horse suffers and all horse owners get educated before actually getting a horse. However, bad things do happen and, when they are caused by someone close to us, we are always better off not feeling resentment about the situation and spreading those negative emotions over to others, but asking questions, educating ourselves about how can we get involved and help, and, most important, being open-minded and kind. Of course, sometimes a person needs a stern slapping back into the reality to wake up and see the harm they are causing, but in many cases these people are not downright evil - they are just ignorant and really don't know any better. They need to be fed the right information and to be inspired, not humiliated. I used to gain my first horse experience in a place that fed me all the wrong information and I actually had a hard time admitting that I could be doing better for myself and the horses! It takes a strong person to face their mistakes without resistance, especially, when these mistakes cause harm to other beings.
So, good luck with helping your friend - remember not to bully her into automatically believing in your opinion. That will get you nowhere. Instead, show a good example, don't ride the horse, give her links to good articles about horse body weight scoring, feeding, health and other important topics. If she truly cares about the horse, she will learn to change. If not - it is not up to you to change her, and you can always contact AC, if things get out of hand.