Post what the letter said. It could just a ganglia. My 9.5 lb son has one. They said it's from twisting his neck when he was being born.
its not always cancer it could be a birth defect or other type of diagnoses
I have seen this on some of my friends, and have had it myself, mine went away pretty quickly, but some others dont. it depends on how long she has had it. can you see a doctor if it gets worse or is painful for you to touch her there?