Breast Cancer, Blister Growth In Breast, Drainage, Hemangioma
Sometimes children can be born with benign and localized skin changes. If as you say she was born with this and its size has not changed in a major way over the last 9 months I am inclined to think it may be a benign cyst. If it has a reddish color to it, it could be what we call a hemangioma.
I cannot think of any genetic association with breast cancers which would lead to a pediatric malignancy, so please rest assured that this is not the case. I am glad you will be getting a definitive answer soon as the surgeon can thoroughly examine her as well as her skin and if a biopsy or procedure is necessary, the pathologist can confirm my suspicion that this is a benign skin change.
I hope this information has been helpful to you. I am available for your followups.
It is my pleasure. I wish you all the best and continued excellent health.