please talk to her, or at the very least make sure she feels she can talk to you.
It is very young by the way!
My mum was to embarrassed to talk to me about it, other than saying it was important to always have clean knickers in case you got run over by a bus 
Then when my period started I freaked out, yet told no one. I stuffed masses of loo paper down my knickers at break time, but the blood still seeped out and I remember EXACTLY the horrified stares of all my class mates at PE (mixed!) at the massive blood stain in my PE shorts (white, of all colours) and the PE teacher was a bloke and didn't know what to do, and sent me to the changing room.
Then at home I desperately tried to wash my knickers and PE shorts before my mum saw them.
the stress! the embarrassment!
I kept using loo paper throughout the first months...with varying degrees of success 
When my mum finally noticed some blood stains (despite my frantic washing) she put a packet of tampax in my bedroom, without explanation, and I remember ending up with the cardboard tube inside me, and the tampon in the loo! I couldn't get it right. 
In the end my dad took pity on me and sat down for a brief chat and told me about sanitary towels. That helped a bit.
Long story, but just to say, please please please do not do this to your daughter.
my sons are 7 and 9 and I have told them about periods as I don't want them to freak out about it if/when they have girl friends.
Why is it such a taboo still? At some of my friends' houses the first period was celebrated with champagne, to honour an important milestone in a girl's life (maybe that is odd too??? still, better)