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.
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.