YOu really need to work on bite inhibition with your pup at this stage in life. At 7 weeks your pup should still be with its mother and litter mates, no puppy should leave for a new home prior to 8 weeks of age and even that I feel is too soon.
May I ask why you are holding her on her back? Are you trying to alpha roll her? If so, why? What are you hoping to accomplish with that.
Alpha rolling is NOT recommended for most dogs, and most people should not alpha roll a dog, if you do alpha roll you have to know when and why to do it.
Get her some vaccines and definitely find a reputable trainer. For now, any time she starts biting, all fun should stop. move your hands away from her and ignore her. Become a statue of sorts.
Courage is being scared to death and saddling up anyways. ~John Wayne