It's funny to me that you mention this! Only because, my sister and I have had this conversation many times... we have 4 girls between us, ages 13, 11, 10, and 8! The oldest is a breed of her own... very independant, NOT girly at all, etc. so she is no help in putting her mom or her aunt through the "little girls becoming big girls" stages! However, the 8 year old has been wearing deoderant for about a year now because she HAS to... she seems to show no other signs of anything except the smell! My 11 year old is just starting to develop so she's not into it enough to say much about. My 10 year old however, has had to wear a bra for about 2 years now... it being a must, every day... but shows no sign of hair or smell. So we have asked a lot... why would my daughter that shows the physical signs not have the other signs... period, smell, etc. But her younger daughter have all of that already?
Our conclusion... it depends on the girl! We have been told by a nurse that the size of your head determins, to a degree, how early things will start for you... something about the gland that controls the hormones, etc. is bigger if you have a bigger head and will control more earlier, etc. I don't know if that's really what is going on, I haven't measure heads! I do know however, that my son who is 7 has to wear deoderant and has for about 6-9 months.
I wouldn't worry about it... she will probly go through some and then it will slow down some, or she could just hit it all at once... if so, be thankful... I have been dealing with the "prePMS" for 2 years now just hoping they will start and get it over with!!!