Please let me start by saying you really got my attention when you said she has continued to pant as if she is still in labor. This makes me worry that there are still more pups inside. It's possible that one is stuck in the birth
canal, or that her uterus is simply too worn out to finish the job. Regardless, this could indicate some potentially life threatening complications.
In regards ***** ***** trying to move the pup a lot and having it in her mouth, that is not particularly alarming. Some mother dogs do that a lot more than others.
The real concern here is how uncomfortable Willow seems to be and the high degree of likelihood she's experiencing some complications from labor and delivery.
Additionally, I want to clarify that it can be dangerous to provide supplemental feeding
to a puppy under circumstances like this. The puppy needs to nurse to receive vital antibodies and nutrition from her mother. Additionally, it is the act of nursing that stimulates milk production; without that, milk production will shut down.
It's also important to note that even well-intentioned owners can end up causing aspiration pneumonia when feeding tiny puppies. The rate of puppies dying due to incorrect feeding is very high particularly when the owner is inexperienced.
Supplemental feeding should only be performed as a last result when nursing is not an option.
You're correct to be worried about Willow. If she were my dog, I'd be calling the vet and arranging for an exam right away - even if that meant at an ER.
I'm sorry to be the bearer of bad news, but I feel it is important to be complete and honest in my answer to you.