Oh, this is just heartbreaking.
Where did you buy her?
If it were me, I would see if she could go back to the mom and litter mates for 7 more weeks. If that is not possible, then you need to treat and care for her as an orphaned pup, since that is what she is.
Maybe you can start a thread in the breeders section to get advice. She is still needing her mothers milk I think, so she might need a substitute.
This just makes me so sad for her. How scared and lonely she must feel. I would keep her with me 24/7 as you are now her "mom", and she desperately needs you.