Worming is the first thing to do. Soaked sugar beet (we use fibre beet, which is quick soaking). There is a horse feed called Ready mash, which you soak with hot or cold water for a few minutes, its really for old horses who have poor teeth, but is great for old goats too, or sick ones!! Live yoghurt will help with her digestion. I would also provide her with ad lib hay if possible, and access to good grazing.
Word of caution - if she is in poor condition, her digestive system will not be able to cope with too much food ....so little and often is probably better than two great big feeds a day. I prefer the weight to go on gradually, although with an older goat, it could take longer than a younger one.