Working at a pet store I see all shapes and sizes of dogs. Some carry their weight differently. I know my chow mix carries her weight much more leanly than other chow mixes. As long as you can't visibly see the ribs, but can still feel them, and there's a defined waistline, you're good. As far as getting her to eat her dog food, you might try going to a grain free food to see if she likes it better. Blue Buffalo Wilderness, Natures Variety Instinct, and Orijen are just a few excellent brands you can look into. (I spend a lot of time reading labels.) Many dogs do fine on cheaper dog food, while other do so much better on a higher quality. Higher protien like Wilderness and Orijen have can also help fill her out if she doesn't just happen to have very prominent hip bones. I know every dog food has horror stories, but these are the ones I've seen the least horror from.
1 Dog- Tina (Chow Mix)
2 Bettas - Sora (Blue Combtail) and Connor (Piebald Cambodian Butterfly)
6 Golden White Cloud Mountain Minnows
4 Three-Line Cory Catfish
1 Assassin Snail - Ezio
4? Ghost Shrimp
5 Rats - Alice (agouti hooded), Zelda (beige hooded), Thyme (seal point siamese), Peanut (mink berkshire), Chakra (black capped w/ headspot)