Q. What my dog can not shit want do I do to get her to poop
A. You could try adding lactulose to her food twice a day. 3-5mls depending on her size. It maybe that she is just a bit constipated but it may also be that she isn't on the right diet for her. Try the lactulose for a few days and then speak with your veterinary practice on Monday and they can advise you on a suitable diets for your dog.
If in the meantime the dog starts to vomit or becomes lethargic then you need to see a vet more urgently as she may have a blockage.