Even though she seems very well in herself, she needs to see the vet as quickly as possible. You can't take any risks, or delay with a little pup as young as she is. I hope she will be okay.
Your puppy should probably be seen by a Vet. This could be swollen lymph nodes from an infection. Could possibly be a reaction to a bite. Thus could be something called Puppy Strangles. You can look that up to read more about it and the symptoms.
I do hope the pup is better and no worse.
Please update.