When do girls start shaving?

My oldest daughter is 10 and in 5th grade. She has recently told me she has hair under her arms! Which panics me because I do not want her to grow up! Lol! When should I teach her to shave? Now because she asks or is she too young still? She only has very faint blonde hair under her arms. My mom never taught me to shave and I did it myself the first time. I ended up with a huge cut and horrible razor burn because I had no idea what I was doing! I want to help her the first time and teach her correctly. So when is it time?