Just, so I get this straight, you rescued this horse from your daughter and her ex husband?
Oh boy, Good for you. I would have a vet out immediately for vaccinations at the least. I would also discuss a weight gaining program. As it was mentioned before, you never know if there may be an underlying issue that is preventing her for gaining weight. Have the vet pull a fecal to check for worms.
Again, good for you for taking on this project. Please keep us updated.
This is what happens when you have democrats in office