I think maybe Many Tears may well be best to advise however, we do have several members who have dogs from Animal Rescues including Many Tears and I am sure they will answer.
For me my little boy was quite bonny as a young dog and I was told by my vet that pure peanut butter was good, so I went down that route, he had about a teaspoon per day, and still has it in a morning on a carrot stick.
It must be pure peanut butter - I use Nuts about You from Tesco - it needs a good stir as oiler than non pure.
The other thing was cooked sweet potato, the chicken and white fish is a good sound idea, but chicken breast as brown meat can make them loose.
Good luck on your new arrival