
Just out of interest, have you considered offering this puppy some fresh raw mince?
I know it is not everyones ideal food but it is the most natural offering a mother dog would make when she starts weaning her puppies.
No matter how backwards your puppy is at the moment, it is however 3 weeks of age, and I would try anything to get my puppy going (without upsetting this delicate tummy and this will be fine).
Try offering a little fresh raw mince, maybe even liquidise it so that the pup just licks at it, maybe even put a little on your finger and put some on her tongue.
I offer 2 to 2.5 week old puppies the taste and smell of raw meat, only such a small amount is required and they are either interested at this early age or not, but by 3 weeks of age they certainly know how much they like it.
No matter what the vets might tell you this is "natural" food and with mums milk is the best way to get a puppy going.
However, it is possible that this puppy for some reason was not intended to survive, and this could be natures way of selecting the strongest !