Teen with uneven breast development

Thanks for the question and I appreciate your concern.It is early in your daughters development so at this stage a wait and watch policy will be the best approach.Into the future if there are psychological issues that arise, you may seek the expertise of practitoners who specialise in adolescent medicine, and these can usually be found at a Children's Hospital.It is impossible to say if the assymetry will become an issue, but rest assured there are networks to help you and your daughter deal with issues as they ariseI hope that is of some helpJeremy Hunt 

It is perfectly normal to have different size/shape breasts.  I would wait until her breasts fully develop.  If at that time there is a concern about asymmetry, then:
1) You can reduce the larger breast with liposuction
2) You can enlarge the smaller one with fat grafting or an implant
3) You can enlarge both but use different size implants
I would visit with a board certified plastic surgeon at that time to discuss your options in more detail.

While most believe that a woman's breasts stop developing by about 18 or 19 years old, they actually continue to develop and change throughout a woman's life. Pregnancy, hormonal changes and aging can all make the breasts change, too. Asymmetry is totally natural and not something you should be worried about. No woman's breasts are symmetrical. Think of breasts as sisters, not twins. 

Breast development continues throughout a woman's life, with a first stage of maturity achieved at 19-20 years old. Asymmetry is also the norm for women, as no breasts are perfectly symmetrical in size and/or shape. For these reasons, I recommend your daughter wait until she is 20 or so before considering surgery, as she still has many years of development to go.

Your daughter's breast development will continue over the next few years. If the asymmetry now does not bother her, it is best to wait till growth is complete before considering management. Most women have some breast asymmetry so it is best to reassess the degree of asymmetry when development is complete.