I agree with all you have been told BUT
You need to take that baby to a vet and have a
complete checkup - it is most likely harboring coccida or some other parasite that is taking its energy-
One of the HUGE problems of taking a baby away from familiar surroundings at a much too young an age is the stress it puts on the puppy which brings on all these other problems due to its system not being able to handle the stress and fight off what ever is wrong .
I am not blaming you for taking that baby at much too young an age but why do people let them go like that ? It makes me so angry to see a baby abused that way
Take care of her and she will get thru this stage but she very well may be sick and needs checked.