It's difficult to tell when they are young, but if you posted pictures that would help alot!
Do you know roughly how old she/he is?
Also if you wanted to see if you can tell, look under the tail near the vent. If there's two long bumps on either side of the tail then it's a boy.
If theres just one bump kind of in the middle then it's a girl.
But yes, thats how you sex a beardie! Under the tail near the vent, vent being the butt
Hope this helps!
Also. . pics would be awesome. We love pics. xD