If you have her on sand, please get rid of it immediately, and use paper towels until you can get tile or repti-carpet. The sand is what is stopping her from pooping.. sand blocks their digestive system. This results in impaction, which can harm or even kill them if left untreated. Regardless of what pet shops tell you, no sand is digestible and it is not safe for bearded dragons, and neither is any other loose substrate.
Next time you give her a
bath with belly massage, put a few drops of olive oil on the tip of her nose while she is in the
bath. Dragons will instinctively lick food off the tip of their nose. You can also use unsweetened applesauce, or organic baby food prunes. This helps your dragon to pass her stool more easily with less straining.. the more she strains, the more she is hurting.
What is the temperature of the basking spot and the temperature of the cool side of her viv? The cool side should be 80 and her basking spot should be 100-105 degrees (110 if she is a baby). If the temps aren't correct, she won't be able to digest her food properly.