Soy is not a good thing to eat if you're female. Probably isn't for males either. My daughter had soy formula as a baby because I was unable to breast feed (didn't produce milk) and she was allergic to cow's milk. I wasn't told about the milk banks that people can use, nor was I given any other help, such as using goat milk from a farmer or any other type of formula other than soy.
I didn't get my period until I was about 13 years old or older (I don 't remember how old I was; for some reason, even 15 years old sticks in my head. I just know I was one of the last ones). Anyway, my daughter just had her first period two months before her 12th birthday. Perhaps that is the norm these days? I don't know. I haven't talked to any moms in her class where the girls have been having their periods, so I don't know. My daughter started developing her breast area starting the beginning of 2011, and has pubic hair already. I'm personally not really ready for all these changes, but I guess when it's time, it's time.
But yes, if your daughter is exposed to a lot of soy products, they can push her into having early puberty. I wouldn't be surprised at all if the soy baby formula and the soy milk we used to drink (because of cow allergy; we quit consuming any type of soy products back in 2008) when she was younger didn't contribute to my daughter's early development.
Right now, I am starting to go through "the change," and I won't touch soy with a ten-foot pole--even though it's "touted" as being some of the "best stuff" you can take as you go through perimenopause/menopause. I take specific supplements and homeopathic remedies instead. I find Maca Root to be especially helpful for me.