She probably spooked up from somewhere for whatever reason, her litter may have been her first, and she may have gotten confused or whatever.
If she has been out by herself long enough, the babies have either died, or the coyotes and crows had a good meal while she was whelping.
Our Indy dog had been out on her own so long that she was actually gray for lack of nourishment. She is a german shepherd, and is a definite tan, but has no saddle ... anyway, she had recently whelped, as your dog seems to have, and she didn't act like she had anywhere to go, either.
Enjoy your new pet <g> ...
I don't know how populated your area is, we are out six miles from town ... in high desert ... if you have a good vet, taking her to him will answer some of your questions.
We took INdy to the Humane Society for a week to see if her owners would show up - - and told them, if no one shows, we want her back. When we got her back, they had spayed her. We took her to our vet and he made a comment "Well, they didn't do her any favors with that spay job, did they?"
I never asked him what he saw or meant, but I knew that I would NEVER take another dog to the humane society ... animals don't live long enough under the best of lives to have to deal with sloppy, careless work. If you really care ... take your dog to a good vet ...
Congratulations, by the way <g>. You got a fine looking animal!