Well you should have a vet check her out.
But if she's going but only a little bit or in hard balls, she may need more fiber in her diet.
I'd really take a close look at her dog food. It may need to be changed.
Until then, you can offer her high fiber treats like green beans. They have no nutritional value but they make your dog feel full and help them poo.
If that doesn't work, see if your vet will okay giving her some Metamucil or Karo syrup. But you should okay that with a vet before hand.
If you do metamucil, start with a half a teaspoon twice a day, in addition to giving plenty of water. *ONLY WITH YOUR VET's PERMISSION.
Increase the dog's exercise.
And really take a look at her food. My Pap when she was younger had difficulty pooping and I found her food had a high corn content. She has trouble digesting corn.
Switched food and she could poo again.