It is an ongoing process that should start when they are very young about their bodies, etc. Answer questions at age appropriate levels.
Communication is key, especially with children.
By 8 years old, she has already heard all about it, she needs honest confirmation from you. If she picks up that you are embarrassed or gets an idea that it is "dirty" ( I am NOT suggesting that you are giving these vibes), she will be less likely to come to you for information. I believe most parents would prefer to be honest and inform their children of what really happens vs the children hearing from children in school.
By 4th grade, our school nurse comes and talks with the girls and boys, separately, about body changes,etc. It is sad but that is the only honest info some children get.
If you don't want to look eye to eye with your daughter, talk while you are driving, walking in the park, etc. You both need to be comfortable talking to each other.... believe me, it is critical when they get older to have a good line of communication established.
I have been a substitute teacher over 10 years focusing on K-5 and I have heard children in 2nd grade discussing body parts, etc. They are curious and they need parents to make sure the information they have is correct.
Good luck...