Helo!! How old does this puppy look ??

She is a pitbull puppy I know she is too young to be away from mom, she couldn't poop unless my boyfriend rubbed her belly with a warm rag :( any guesses ? The brindle is my 6 month old male pit, for comparison. We got him at 7 weeks and he was probably 5 times bigger than she she is now 😕😕 (my boyfriends mom adopted her for his little brother but he doesn't Take care of her.. so she's giving her to us) she is a sweetheart & we know we can take good care of her