Hi E.,
You might take her to the doctor and have him/her check it. My daughter had a bump on her temple that just appeared when she was around 8 months old. The doctor said it was more than likely a "dermoid cyst", which is normally not scary, bothersome or dangerous. However, the doctor said any bump should be check out further, just in case. He referred us to Childrens Hospital and 2 days after her 1st birthday, she had it removed. I have to say that the people there are the most wonderful and caring I have met. They did everything to reassure this nervous and worried mommy. My sweetheart is now 18 months and you cannot even see the incision mark, the plastic surgeon was amazing. They sent it to the lab to test, just to be safe, and sure enough it was a dermoid cyst - non threatening. You can check out "dermoid cyst" on the internet but all it is, is a combo of cells, hair, sometimes bits of bone, that have collected into a lump. They pretty much form while in-utero and sometimes dont show up for years - as may be in your case. The reason they took it out was to make sure that was all it was.
I would tell you not to be worried but you are a mom and I know how it is. You are right, it bothers you more than her. Just get it checked by her doctor and see where it takes you. Again, if it is a dermoid cyst, there is nothing to worry about and you can have it removed - try to see if they will refer you to Children's. I think they are just the best and all they do are kids so they know how to act towards them. They are amazing there.
Good luck and I hope you all the best.
L.