Normally there are more than one baby.But if she is a small breed or this is her first litter there may be just one baby. Labour is normally only about 15-20 minutes and she will give birth to all the babies very quickly. She could have a stuck kit, take a look at her vent area and also feel around to see if you can feel any unusual lumps. She may have to go to a vet to make sure all the babies are out.
What kind of rabbit is she?
Is she seperated from the buck? Does can get pregnant immediatly after giving birth, but it is very hard on her and the other babies. The babies will have to be weaned at 4 weeks when the second litter is born rather than at 8 weeks, which is best for them.
Did mom build a nest with lots of fur?
Does the babies belly look round and full or does it look shrunken and wrinkly?
--Dawn