If she has been pushing hard for an hour then I'd call the vet now.
It may be the vet will be able to help deliver the pup or as happens for many breeders the pup may arrive as you drive mom down the bumpy road
These sites go over the whelping process including pictures and when to see the vethttp://www.dogbreedinfo.com/whelping.htm
I usually start being concerned if there is hard labor for more than 20 minutes with no puppy arriving.
When you get to the vet ask for an x-ray to see what is going on after the vet does an exam. They are likely to suggest an oxytocin or pitocin or 'pit' shot to help her push harder. I would not recommend letting them do that until you have proof on x-ray that the puppy is not too big for her to deliver. The shot will make her contractions harder and could thus rupture the uterus if the pup can't fit down the birth canal which will endanger the other pups.
If the pup is stuck or too big you may be looking at a c-section to save the mom and other pups. You might lose the stuck puppy but with luck you won't lose the rest.
If the vet says wait another half an hour just say no and that you want the dog seen right away. If your vet can't do it this site may help you find an emergency vet
to work with.
Hope this helps you!