Welcome to the forums! Your puppy at 6 weeks is too young to be taken away from her mother and littermates. It is illegal to sell a puppy before 8 weeks of age.
She should be spending time with her littermates still, and learning bite inhibition. You may have problems later because she was taken away too young.
She should be eating a top quality large breed puppy food at least 3 times per day. ....till around 5-6 month of age. You can go to two meals after that. Please take her to your vet and make sure she is healthy and has been wormed...it sounds like she has not come from a good breeder.