@house I feel for you, but you need to get into “professional service provider” mode with this owner and her 8 horses. You are in this boarding business to turn a profit, slight though it may be. Is your board income more than what you pay out for hay and farm expenses, with some dollars for your work time?
You need to realize “It is not YOUR job to subsidize HER horse habit! Not YOUR responsibility!!” Repeat that several times each day and as go to you talk with her. Being sympathetic, overly helpful, will let her suck you dry, take away all your enjoyment of being out with the animals. You get burned out with HER issues! Trust me, they never stop.
You are a horse professional, trying to stay ahead of your expenses just like various other professionals. The Farrier, Vet, Trainers do not cut costs for their services or they go out of business!! We have been in a horse service business for years, you provide what they contracted for, or YOU start losing money! No favors, no discounts, because they will just take advantage of you.
This is hard at times, you do feel for the animals! But users don’t give back, monetarily or even with labor time, to help you back, should you need it. If she can’t pay for Vet services to at least learn WHY horse does not gain weight, then fix what she can, she needs to sell some horses!
As mentioned, there are ALWAYS more boarders to fill her spots. You won’t lose money if she left because your expenses will be cut at the same time!
Sorry, but it is time to rewrite any contract between you and boarder, be more detailed on feed quantities, her SPEEDY Vet responsibilities when horses go downhill. Added board costs for extra hay and grain, time spent with extra care in HER injured animal.