What can I feed My dane that she will gain weight?

I have a 2 yr old female Dane, who is very picky , and very skinny. I have put her on TOTW, she doesnt like it, I put her on Nutures Recipe, didnt like it,Blue Buffalo, didnt like it, Pedegree Large breed,.....nope. I have her on purina pro plan for large breeds, wt real lamb peices in it, she likes it, but not picking up weight. Vet checked, nothing is wrong wt her, he says offer her more food,keep it away from her and feed on a schedule, she lost weight. Ive tried yogurt,cottage cheese, she eats the food more, but is expensive to keep up, and I dont wont her to expect it every time. What can I do to help her gain weight? Feed her raw? make her rice? (which I know is a grain but...Im reaching here) Please help me out! Oh and she has been wormed....