DD12, soon to be 13, was diagnosed at age 6. Her history: very hairy legs at age 2; needed deoderant at 4 and started underarm hair at age 6. Our pediatrician was aware of all of this and sent us to a ped. endocrinologist at 6. Bone age studies were done and she was advanced by 2 years. We were just taking a conservative approach until dr. (specialist) said it wouldnt' be a be a big deal if she goet her period. I was shocked at his attititude. I can't handle it some months at my age! Also, once you start menstuating, you have pretty much maximized your height. Hormones close your growth plates.
We then went to Univ of IA to a fabulous ped. endog. At age 7 1/2, she jumped 2 years on the bone age and started to get pubic hair, so we started Luperon injections every 3 weeks for 2 years. Fortunately, I am a nurse and could give them at home, but did the 1st few at the dr office to get her used to it. We kept at the injections until her bone age and actual age were just a few months off.
DD had her first period just after her 11th d-day, 5th grade. It was irregular for the first year, but has started to regulate some. Her height is approx 5'4" She was more cognitively able to handle the hygiene needs of having her period, esp at school. Her height is also maximized, considering her parents aren't that tall.
For us, the Luperon was the right choice. The most important thing is to be comforatable with your child's health care team. Ask questions and don't let the alarmists get to you. If you don't understand something, ask. Every child will go through puberty at a diff time in their lives, so their really isn't a "typical" age. The bone age study is the determining for the diagnosis.
Good luck to your friend and her daughter. PM if there is anything else you want to ask.