It is very sad that your horse was abused, however I am curious as to how long you left her at the farm before you decided to go back for her and what your arrangements with the barn were? Did you pay board for the time you weren't able to work? Perhaps I misread, but from what you have written, I get the idea that you left for a while then came back at some later time to get the horse?
I know it might be hard to hear, but you you are just as responsible for those injuries to your horse: why in the world would you have "worked off" board for someone who treated your horse so miserably? That is enough of something "coming up" that I'd find another barn and work off board, or find my horse a new permanent home with people who loved her if I couldn't find and afford better for her. Why would you have left unexpectedly and leave your horse there under ANY circumstances, knowing the people were abusive? Something about this story doesn't add up to me, I'm sorry.
I hope she has found a loving new home with people who can afford her, love her, respect her and treat her right. You should be happy for her if she has.