Ginger is right...this is any important behavior to stop and stop soon.
Dr. Suzanne Hetts, a certified applied animal behaviorist, as written in her book "Raising a Behaviorally Healthy Puppy" to do just what ginger has said. In fact, in often works to ignore the behavior and walk away from the pup. After she has calmed down, go back to play with her and if she acts "nice", she gets the reward of playing with you.
Dr. Hetts is also available for questions in our Ask the Vet expert forum under the Pet Behavior Forum.
This has to be stopped, as what she is learning now will stay with her for the rest of her life, unless checked.
I think she has been taken from the litter too young. She has not learned early lessons which she could only learn with her litter-siblings, and her mother.
Biting is natural for a puppy, and with its siblings and mother, a pup learns how a gentle bite is playful, but a harder bite brings either squeals, or chastisement(from the mother) Usually, when playing and bites get too hard, the other pup, the one bitten, will squeal, and usually that stops the pup biting immediately.
I tried that with the dog I had before (a Jack Russell) When I first got him he was nearly 8 months old, and was still biting too hard. Every time I felt his teeth I squealed like a pup that has been hurt. It did work. He stopped biting hard. He learned how far 'play' is meant to go without it getting serious. You could try that.