P.:
good morning and welcome to mamapedia!!!
It sounds like she has a swollen lymph node. When lymph nodes are working overtime to fight off infections, they do get swollen.
My youngest son's lymph nodes can get so swollen they look like the nodules on Frankenstein....not kidding. He isn't running a fever, he isn't sick, his body is working.
I know how scary it is to see a lump on your child. I really do! Over the next several months - while Spring turns into Summer and the pollen runs over her, she will most likely still have the lump.
make sure she drinks a good amount of water to help keep her body flushed out.
Good luck!