A momma dog will need a nutrient-rich diet so she can keep up her energy levels while nursing her pups. A performance diet or puppy food will help her maintain her weight and balance her mineral loss while she's pregnant and nursing. She can have treats, but give her high-calorie, healthy ones.
Salmon and sweet potato treats are generally healthy treats; if you can't find it at your local pet store, you can make your own. You can cook meatballs made of lowfat ground hamburger meat, and offer them to your dog as treats or as a part of her diet. Offer eggs, chicken and other meats, as well.
Treats Should Be Healthy
High-calorie doesn't mean junk food and candy. Make sure that you know what you're giving your dog. You want to make sure you are not providing her with loads of carbs and fats but with well-rounded treats. There should always be a real meat source in the treat; if you buy commercial dog treats, make sure they are not made of a byproduct or meat and bone meal.