Alfalfa is a good choice because it helps buffer the stomach. I don't think she's added substantial weight but she atleast looks happier and her eyes have life back in them. Good job just keep truckin...she'll get there.
Oh also...have you thought about a horse chiropractor. Might be hard to find a certified one in your area. But my horse's chiro has suggested that some hard keepers need an adjustment to help gain weight. Her sacroiliac area (pelvis top of rump) certainly looks awkward to me.