I'm not trying to be rude here poster of the thread. But I'd stop posting, you're digging yourself a huge hole.
And honestly. If the board is only 60$ a month. That would kinda almost be a red flag to me. Any barn with something to offer is gonna cost you into the hundreds. I have an idea of whats going on, its the blame game. You think your friend didn't do as asked and now your mare is skinny. Maybe your mare is just a hard keeper?? Checked her for worms? Teeth? Sores around her mouth? If your friend is saying he/she did what you asked. Your mare shouldn't have become skinny, if you were telling him to feed the right amount in the first place. When in this situation yes you were on bed rest and couldn't go out and check, so I kinda am sympathetic to you. On the other hand, about the friend you should have used better judgement and seen the mare was getting skinny and fed more. You say you have experience lots of it around horses. If you knew the mare was skinny you should have been feeding more and not complaining to the owner about it.
I say this in the nicest way possible. If you do wanna jump on me feel free.