I'm happy that you have asked me to assist you with your child and hope that you can benefit from my many years of helping parents like you. I agree with her doctor, as disturbing as this usually is for mothers and dads of preteen girls! It is normal for breast tissue to develop as the very first sign of puberty, usually right under the nipple and usually on one side only for a few months. This can be pretty sore at times as the tissue develops but often that is the only thing that happens for a while, with pubic hair to follow, but thankfully at least 18-24 months for her first period. You need not do any further tests or exams and just let her doctor follow it as long as there is no redness or discharge from the nipple.