It's a normal stage - take a look at JanD's thread below about Bobby chewing for some pics of Adolescent Cocker Carnage....
While she has all of her adult teeth, the molars are still settling in, and this can give some dogs a seriously overwhelming urge to chew. Make sure she has plenty of things she can chew, keep other things out of her reach and also ensure she has plenty of mental stimulation, as boredom can increase the desire to chew (chewing can also be a stress release, so do ensure there's no anxiety at being left of similar at play).