A few months shy of my thirteenth birthday, I got my period for the first time. When I told my mother, she slapped my face on both cheeks and said, "That's a custom in our family--so your cheeks will always be red."
She then handed me a sanitary napkin and belt and told me what to do. I remember fumbling around, not liking this unwieldy way of dealing with what should have been simple. I also remember we didn't talk about this new wrinkle in my life very much, other than to say it meant I could get pregnant and needed to be careful (whatever that meant).
My mother was old school and not versed in talking with her kids about sex, so I had to get most of my information at school or from my older sister and other friends. Luckily my sister was cool about sharing her thoughts and experiences with me, but she was seven years older and it wasn't always easy to track her down.
I'm bringing this up because I would have loved to have more information and support about what Anne Frank used to call her "sweet secret." I'm very glad we are a more open society than we used to be, though I know that in other parts of the world, young girls are not getting information that could help them deal with their sexuality and gender.
I resolved when I grew up I would TALK to my kids frankly about sex, and I hope my son would say I kept that promise. It felt scary at first; he was eight when he first asked me what an orgasm was and I have to say I was not prepared for the question. But I did try to answer him matter of factly and give him age-appropriate information that would at least respond to some, if not all of his questions.
The thing I have that my mother did not was a lot of books (and the internet) and suggestions on how to talk to your child. I wish she had been able to access that because it would have helped us both so much. I do remember feeling happy and excited on the day my first period came; and that at least is an indication that the occasion was a good one. All I know is that it should never be an occasion for shame.
If I had any advice at this point besides being frank and friendly, it would be NOT to slap your kid's cheeks if she tells you she got her period. Her cheeks will be red enough.
If you're looking for help about what to say, I found some posts for you:
Talking to Your Kid About Menstruation
5 Tips for Talking with your Daughter About Her Period
When (and how) to Talk to Your Daughter About Periods
Young girl photo: Igor Gorshkov