Reddit reviews The Care & Keeping of You (American Girl Library)

Not sure if anyone has said this yet, but the book The Care and Keeping of You Vol. 1 from American Girl is extremely detailed and helpful when it comes to things about puberty such as info on female anatomy, what tampons and pads are, what types of bras and underwear are good for you, how to care for your hair and body, etc. I bought it for my 10 year old sister upon her request and read through it myself. It's very open, informative, and body positive. It doesn't talk about sex and sexuality much at all, but maybe that's something that other volumes get into? I'm also unsure if it's sold in your native language or not, but even if it's only in English, it might still be a good thing for you to read if you want a detailed and informative source for what's to come.
https://www.amazon.com/gp/aw/d/B00BHI2GW4/ref=mp_s_a_1_1?ie=UTF8&qid=1491837456&sr=8-1&pi=AC_SX236_SY340_QL65&keywords=american+girl+the+care+and+keeping+of+you+1

I'm a bio and a stepparent, and I feel like the best time to have The Talk is when it's natural and doesn't feel forced, regardless of who ends up having The Talk in that moment. As your SD gets older, you'll discover The Talk is not just one talk but in fact comprises many, many conversations about her body, puberty, sex, relationships, birth control blah blah blah that may be had with any number of adults: you, bio parents, teachers, other friends' parents, whatever.

I wouldn't bring it up to BM. If it comes up later and she freaks out, whatever. Deal with that if it happens. You can't unsay what you said, and frankly I think that starting sex-positive attitudes when the opportunity presents itself is way more important than what bio mom thinks.

Also, if your SD is showing interest in the subject, might be time to invest in some books. I think
Care and Keeping of You is pretty good for her age range.

First know that plenty of parents (moms and dads) struggle with how to start this conversation with their daughters. There is the general awkwardness of the topic and the idea that a little more innocence is lost.

This book is a good place to start and you should read it first American girl - care and keeping of you

Also, are you there god, it’s me Margaret is a classic preteen that delves into topics for things she is likely going through

Depending on your relationship you can start explaining what will happen to her and ask if her friends have talked to her about this kind of stuff. Expect some squirming and go at her pace. Keep some nice quality pads on hand for her as well. They also make period panties which are expensive but worth it - accident do and will happen to everyone

Finally, as others have said, talk to a female relative closer to her in age that she can trust and see if they can get her to open up.

When that days comes give her a big hug, it’s stressful at first. Good luck

at home: my mom gave me 'The Care and Keeping of You' book that explained all of physical things about puberty. Still didn't put together what sex exactly was, although I knew it was when sperm hit egg. (I was quite sheltered.)

public school: had the "this is what sex is" talk in fifth grade health class, then we split by gender to learn about things specific to our anatomy. In middle school health class, we had various units on anatomy, STDs, and the different types of contraception. (We were told that abstinence is the only foolproof way to prevent pregnancy.) In 8th grade, we also got to take home a robot baby for a night to scare us into not having a kid. (I think it worked, we only had two or three pregnancies out of 1,000 kids in high school.) I named mine Philip and managed to not kill him. We were told by my health teacher in 8th grade that despite the fact that most of us said we'd place an unexpected child up for adoption if in that situation, most of us would have an abortion. (She also told us that someone in our class of 22 would die from AIDS, which, given the statistics of the state seems pretty unlikely. We've had more deaths from heroin overdoses.) High school was basically the same as middle school, I think.

CCD: I do not recall anything said about sex, but I also stopped going around sixth or seventh grade as I had been confirmed when I was seven. My parents didn't force anything.