For a dog to be healthy, you should be able to feel but not see the ribs, same goes for the back bone. What I would do is take her to the vet and see if it's anything medical. If it is not, then I would use what I use to get my dogs to gain weight. One of my male Newfie's got poisoned by Eukaneuba dog food when he was a puppy. It nearly killed him and every since then, he has not done well at eating. I scoured the internet and different vets and nutritionists until I finally found something that he will eat and that help him gain weight! I give this to all my dogs when they are a little under weight. But I love to use this during winter, as it really helps them keep weight on, as it takes more energy to run/play in the snow.
They are called : Satin Balls
This is the original recipe:
10 pounds hamburger meat (The cheapest kind, the more fat, the better)
1 lg. box of Total cereal
1 lg. box oatmeal
1 jar of wheat germ
1 1/4 cup veg oil
1 1/4 cup of un-sulphured molasses
10 raw eggs AND shells
10 envelopes of unflavored gelatin
pinch of salt
Mix all of it together and form into balls to use as treats or mix into dry dog food. You can freeze the rest.
However, if you just want to try them out or have a small dog, this recipe this scaled down version (1/10th or the original).
1 pound cheap hamburger (for high fat %)
1 1/3 cups Total cereal
1 1/2 cups uncooked oatmeal
1 raw egg
6 tablespoons wheat germ
1 package Knox unflavored gelatin
2 tablespoons oil
2 tablespoons un-sulphured molasses
Pinch of salt
The only thing I suggest you change is the oil; vegetable oil has no health benefit, so substitute it with an oil that does (like flax seed oil which is high in healthy omega 3s).
Here is the link:
Satin Balls Recipe
I hope this helps!