Re: Separate grazing or in a herd dropping weight
I have a 23 yr old pony who has to be separated, due to being herded by my other horse, constantly. This aggrivates his arthritis, so I normally keep them apart at night, and together for at least part of the day so they can groom each other.
So perhaps try a bit of each, out on her own to feed her up, and in with the others for some of the time.
I think it's getting the balance right, sometimes you also have to ignore the fact they want to be with the others, as with my pony atm, who is permanently separated for now due to an injured leg and then having gone down with laminitus! He still looks longingly over the fence at his companion, and I just have to ignore it, as theres no way he can go out with him!