How to help my bearded dragon?

You need to give more info about your set up for her. Do you have a UVB light and a basking temp of about 95 F available for 10 - 12 hours a day? Incorrect lighting and temps can easily cause stunted growth, ans eventually more severe medical issues. If you a re using a coiled/compact UVB bulbs, or if you don't have a UVB light and you were thinking of buying one, I highly recommend that you switch to a long tube UVB bulb/don't buy one. Coiled/compacts are known to cause severe eye damage and/or blindness in reptiles, not to mention they have trouble maintaining UVB output over time (you'd be lucky to get 4 - 6 months out of one, whereas a long tube should be replaced, at minimum, yearly.)

Have you taken a fresh stool sample to a reptile vet and have it screened for intestinal parasites? An intestinal parasite infestation can also cause stunted growth in reptiles. Many feeder insects, including crickets, are often carriers of pin worm, so it is a good idea to get your bearded screened by a vet regularly.

How much, how often, and what exactly are you feeding her? Here's a couple of good guides that can point you in the right direction as far as diet content is concerned, as well as general care info to make sure that your set up is correct:

http://herp-info.webs.com/beardeddragon.htm

http://www.beardeddragon.org/articles/caresheet/

If ur under feeding her....then feed her more then usual