It sounds like she is just too young, I have 7 week old puppies now and they still drink from mom although they are eating puppy food just fine. She is crying because she misses her momma and litter mates. Remember shes small so she won't eat much at one time, just make sure she eats and drinks plenty of water. Try filling a soda bottle, 2 liter one, with very hot water and then wrap it in newspaper or towel for her to snuggle with for warmth. good luck with your new puppy, although I am not impressed with your breeder letting her go so young
Not your fault, I know.