This sounds like an upper respiratory infection, or more specifically, rhinits. They can be cause by viruses and bacteria.
With your dog being a puppy, I would recommend having her on antibiotics to help resolve the problem. This will not cure a virus, but it certainly will kill bacteria, and prevent this from going down in her lungs and causing pneumonia. You will most likely need to see the vet to get her a prescription for the antibiotics.
In the mean time, you can give her some children's Benadryl. If you buy the pills she can have 1 1/2 pills every 8-12 hrs. If you buy the liquid, give her 1 1/2 teaspoons every 8-12 hrs. This might help her breathe through her nose better, but she will need antibiotics to help rid her of the infection also.
Let me know if you have more questions.