Provided you take her to the vet within two days of being mated the vet can give an injection to prevent her having puppies. Any longer and you are stuck with the problem I am afraid.
If they have the injection there can be some problems associated with it, but as your bitch is only one year old I would recommend you go for it, as that is much too young to breed from her as she is only a baby herself.
Please have her spayed as soon as you can after she has had the puppies, or if you are lucky enough that she is not pregnant after all then get her spayed in a couple of months time.
What breed is she, and what is the male?