Goat feeding?

Have a goat that is extremely under weight and not eating very well need some help. She is about 40 lbs and i am currently feeding her sweet-tex 16 grain (16%cp, 2%fat, 7%fiber, 1.5% Ca) i am also feeding hay. She doesnt eat much and i am trying to get her to gain weight. How much should she eat and how can i get her to gain weight