Better They Learn It From Their Friends …
This is a parenting rant; this is more conceptual than particular, and directed to more than one person.
“But she doesn’t know about that yet” is not an answer. That’s when she needs to know it: before she needs to know it. If she already knew it, she wouldn’t need you to tell her. So tell her now, when she doesn’t need to know it.
The time to tell her is when it’s a strange rumor about someone’s friend’s cousin at another school. She’s fishing for information. If you dodge the question, she’ll let you. And she’ll know not to ask again. “You can talk to me about anything” is a platitude. She’s not stupid; she knows it’s a platitude. She knows it’s a platitude because she sees that you don’t want to deal with the questions when she raises them. When you dodge, she knows she can’t talk to you about anything; only things you’re ready to talk about. That’s why you shouldn’t dodge it.
Even in what passes for comprehensive sex ed, they won’t cover it. Popular culture won’t teach her, they just pitch jokes that assume knowledge. So that leaves her friends, who are all 14. I didn’t have much access to accurate information then and neither did you. Do you think they are much better?
If you wait long enough, you can avoid the conversation entirely. She’ll get inaccurate half-assed information from somewhere else. This is not the best outcome, though it may be the least embarrassing.
Nobody will do your job for you. If you don’t do your job, it won’t get done. Not the way it ought to be, anyway.