No amount of fore-thinking is too much thinking when it comes to knowing what's coming down the pike for your kids. Just want to straighten that out. I have 5 and I've been thru that quite a bit, with a lot more coming.
Any conversation similar to "why is that kid staring", we've had with our child in question well ahead of the time that they might ask. I'd say that we're highly proactive with our kids, setting up rules and imparting information before such issues come to the fore.
You're thinking ahead. That's good. Take advantage of it and act ahead.
To answer the question about HOW do you do it, I think it starts by taking your comfort and tossing it in the bin. A lot of people avoid these conversations because it's uncomfortable. I understand it, but it's a goofy reason. It does nothing but get in the way of, as you said "reality".
The wife had the "feminine hygiene" conversation with my oldest daughter (my eternal gratitude for that), but we both talk to her about the social aspects. It's an ongoing conversation for us and likely will be for several years.
So my daughter is huge for a 12 yo. She's 5'9" or something, D-cup, 150# or so. I forget how it started, but we were talking about nothing one day and I felt an opportunity. So I just told her flat out "You've a large chest for a girl your age." She didn't scream or cover her eyes or any nonsuch... this is the relationship I have with my kids. she just said "I know, that's why I won't hug Mikey cuz he's short" and then we just talked. I told her about how boys will treat her, how men may treat her, and how she has my permission to knock the everloving crap out of any kid that puts his filthy mitts on her. She told me about her friends, other girls in her classes, and how she's caught boys (and girls) staring, but she just blew it off.
The point is that I treated it as nothing special. I just flopped it out there as part of whatever the conversation was. I didn't alter my language, mood, location in the house, nothing.
I submit that that's what you do... Just talk plainly. Don't make a big fuss about it because that will make it awkward. Just tell her what you know in plain words, keep the conversation simple, and listen to her (both verbal and non-verbal) as she converses with you. You may even learn something.