Hi,
Please don’t worry! First of all, the chances that this could be breast cancer are extremely doubtful. Sometimes a little cyst or pimple can form on the areola or nipple.
The nipples contain glands like the skin of the face. If the pores get clogged and secretions accumulate, this can become infected and manifest as pimple. Tell your daughter not to touch it, she should keep the area clean, apply warm compresses and see if it goes away in a few days. If it does not, then you could take her to see her doctor or a dermatologist who can prescribe a medication to prevent future development.
Best wishes to both of you....