How terribly stressful for a dam. I am glad you have her. Make sure she is not too warm, if she is panting, get a regular digital thermometer and take her temperature rectally. If she is up over 103.5 or 104, I don't know that I would wait to go to the vet at all. As she is older, she may have just been tired out and failed to get them all out, retained a puppy, etc.
You need to know if she is running a temperature. Her temp should be 101.5 - 102. She is stressed. But if it gets much over 103, it could be life threatening.
If they gave you food, keep her on it for a day or so, and slowly transition to a good adult kibble. Adding some Dannon's regular (not low fat) yogurt, and some fresh raw chicken, and some eggs (I cook them, boiled or nuked).
As for the adult kibble, choose something that you can wean the puppy onto. I use Diamond Naturals Adult Chicken and Rice. But there are probably better foods out there. Wellness maybe (not Core) -- don't go for grain free, and if you aren't intending on keeping the puppy, pick something that is relatively easy for someone to find.
Heidi Ho, Odie
Joy-Joy, Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.