Word of caution here, OP.
I get that you're young and all, but you should be really careful about what you say on the internets. Because once it's there, it's there forever. I would be very very careful regarding accusations of "abuse" because those kinds of things can and will come back to haunt you. You never know who is reading the board and you've given enough information in various posts that someone could put two and two together. As someone who leases a horse, you need to be as diplomatic as possible in any form of communication regarding the horse because while most owners won't necessarily get upset, there are some owners who do not like someone essentially smack about 'em talking behind their back.
I'm not saying this to be mean or anything, so don't take it the wrong way, but I do speak from experience, knowing that things I've said online can affect me. Long story short, I had posted a reply to someone online asking about riding lessons, had mentioned my former trainer as a possible contact and said "old trainer" and my former trainer did manage to find it online in a web search on her name a few months later, she wasn't mad, she teased me that I called her 'old' as in old rather than old-no-longer-training-with but you can see how things we post do have a way of coming to the surface even if we think the internet is anonymous.
Honestly, I think if you've gotten to this point where your relationship with the owner of your lease horse is what it is now, my advice is to walk away. I don't know if conditions at the barn are as bad as you claim, the forum here only has your word to go on it, and there are always different points of view regarding any situation, and I know you mean well, and have the horse's best interests at heart, but there is some bias in your relating the situation here on the forum. You would be better served leasing or riding in a more positive environment rather than letting resentment and edgey relationships sour your riding experiences. Trust me, I've been there. And it's hard, but sometimes, you just need to walk away.