A related discussion,
lump in breasts was started.
I am trying to remember how old you are when you start to develop? I say this because when my oldest daughter started to develop she also had a lump similar to what you describe. I panicked as I'm a bc survivor and took her to the pediatrician. They told me it was a node and it was not uncommon for girls to start to develop unevenly like that. Sure enough it was the beginning and the "lump" went away. We laughed about it later.
Dear luvh20, Given your daughter’s age it would be unusual that this lump would be cancerous, and may very well be because of the injury. However, having it checked by her pediatrician to ease your mind is fine.
When I was 15 years old, I as well found a lump in my left breast. Go get a biopsy done asap to make sure it's not cancer.
I had the option of leaving it and finding out it would only develop into breast cancer, or get it removed asap.
I got it removed and have never had a problem since.
To my knowledge, breast cancer has never been reported in anyone as young as your daughter.