Don't feel guilty. You have given him a home, and are doing your best too help him through this. It will take time, but he is a very young puppy, so however long it takes, it will be worth it for the rest of his very long life! If it all goes well today, the neighbor can report in, and then after a few days like this, lessen her visits gradually. Does he have a crate or bed that is is "safety" spot?