So sorry to hear this Lyn, has she indeed been checked for hyperlipemia?
We had a mare with that last summer (high liver enzymes, and an undiagnosed infection). She was one month post foaling and stressed if her baby wasn't right with her, so weaning wasn't possible as we were afraid that would throw her back into hyperlipemia. Sonnet dropped 50 lbs in in seemed a matter of days.
The vets weren't sure she was going to make it even when she came home, and that was their thing - keep her eating. As we had her on antibiotics it was important to monitor for diarrhea and keep her eating.
We gave her free choice green grass, shaken alfalfa leaf, soft grass hay, Equine Junior and Folac pellets. her appetite was zero for the longest time, she would just nibble but we just kept encouraging her. It was really hard as her baby was taking so much out of her, but the alternative of weaning and the stress - it was hard - so we fed them both alot. Sonnet and Comet literally lived in our backyard for over a month, and took three months to put back in the herd. They're fine now, but the first few days I was sure we'd find Sonnet dead and have an orphan to raise.
We'll keep Fancy in our thoughts and prayers.