Can I shave my puppy dog?

Our dog is about 9 months old, and she's a smaller breed. She has black hair, which is wavy and getting pretty long (1 inches). So long that she's getting "bumpy" or "lumpy" hair, especially on her tail. We don't know what kind of dog she is exactly, but we believe she is a mix of terrier and something else...Would it be OK to shave her hair, or should it be left to grow out? What happens to a puppy who gets shaved and shouldn't (because of the breed)? Can all dogs with medium-to-long hair be shaved?