You need to get some puppy formula for her, and some advice from a vet unfortunately, and it may be wise for the vet to actually see her if she is looking unwell in any way. DO NOT try to give her any other milk such as cow's milk etc. By getting her the right care right now, you may save her life.
But do also be prepared for the worst, while hoping for the best, as some puppies don't make it.
I wish you well with her, bless her.