I was 12, my daughter was also 12.
I had a talk with my gynecologist about this last year because of an article I read about a 11 year old having a baby!
He said the girls are developing younger and at his medical convention it was a big topic. They are not sure if it is all the hormones/additives in foods now or that children are developing earlier because of environmental changes?
Interesting though...I would take her in for a complete exam..give you piece of mind!