Why does a female dog neglect one of the litter?
She moved all the others and left one. I took it to her and she will not have anything to do with it. It seems healthy.
Is there a way to get her to re-accept it?
This behaviour has to do with its nature, and the fact that in the wild, a mother (or parents) will pool all their resources to the offspring that they feel will have the best chance of survival.
So if most female dogs have a natural mothering instinct, why would they reject a puppy? You can blame Mother Nature for this. In the wild, only the strong survive. Although dogs have been domesticated for a long time, that knowledge remains alive within them. So if a mama dog is rejecting just one puppy out of a litter, chances are there's something wrong with that puppy — maybe a deformity or a serious illness that makes it unlikely he'll survive into adulthood.
Since Mom has other puppies to care for, she will reject the runt who has little chance of survival so she can concentrate on taking care of the rest. When this happens, only human intervention—including bottle-feeding and a visit to the vet—can save the puppy.
You said there seemed to be nothing wrong with the dog - it could just be that he is smaller than the rest, or the runt of the litter.
It seems that it may be difficult to get the mother to re-accept the puppy, if this is at all possible - in her mind she does not want to 'waste' her energy on a puppy that she does not think will survive - therefore, as stated above, it is best to look after this yourself, and get information from your veterinarian on how to bottle-feed the puppy and make sure it gets the nutrients it needs to develop properly.