unusual breast growth

My thirteen year old daughter, has a significant difference in the size of her breasts. It can be shown easily, and she feels very uncomfortable with it. I don't know how normal this is, and I must admit I am quite worried, besides since it has become easily shown she feels bad , she doesn't want to go to the doctor and she avoids wearing what her peers do and this makes her feel even worse.   Is it normal ?  Do I have to take her to hospital ? Is there any medicine or hormones or something else she should be given ?   Or we have to wait until her adulthood when something more radical , as a plastic surgery, corrects this ?                                                                                                             Thank you very much in advance                                                                                                                      for your answer .

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