Early? Some girls get their periods at 9. Even if your daughter doesn't she'll know kids who do.
First, I don't reccommend a talk at all. Ever. It should be a conversation. Honestly, I think it should have started when she was about two. And maybe it did. Did you tell her that she's has a vagina? Labia? That boys have a penis?
(Quick side note,,,My youngest three have language problems. I taught them, but their pronounciations were unique. About 3 years ago, we were discussing women's parts and one of them said something about China. Wait, what the heck are you talk ing about? I queried. China, you know, boys have a penis and girls have a china. So, I explained the error. I watched my then 13 yod face as the realization came over her. Then she explained why she'd thought it was china. (Please, don't bother with the geography lesson!) "China is on the bottom of the earth, and this part was on the bottom of me!" I almost wanted to start calling 'it' china too!)
Ok, so if you haven't done the basics, get a book, it will help. Lots of them are friendly and easy. Get one that YOU are ocmfortable with, you'll be answering a lot of questions.
Then, the darn tv is a great help. Watch any sitcom, and explain what they're talking about.

Seriously, things come up even on kids channels that open the lines. See if soemthing does. Or start a conversation in the car. No one can escape. Or while doing laundry. Hey, DD, you know why Mum has these pretty pads? Or, do you kknow where babies come from? Would you like to?
My nephews explained sex toys to my daughters when they were 8! I wasn't happy. Then again, at least THAT conversation is out of the way.
I explained noctural emmissions (on my best behavior here!

) to my son in the car, because I knew we were getting there and the opportunity to explain hadn't arisen naturally. He never spoke. Never looked at me. Got out of the car when we got home and never mentioned it again. But he knew, and he knew I knew, and he wouldn't think he was bad or sick or anything.
Be graphic. I mean, don't sugar coat it. Kids need the truth, all of it. But not all in one day. "mommies and daddies lie down together and kiss and cuddle in a special way' is fine at 8, but but 12, they'll need much more, well, detail.
Good luck. Kids should come with a direction manual! My son was absolutely fascinated with HOW the baby got OUT. I mean completely obsessed, at age 5. All those explanations, and then a c-sec! That would have been soooo much easier to explain!