I had the talk with my daughter when she was about your daughter's age.
I got my first AF at 12 and I was very developed by then (wearing a C cup bra )
My daughter is 12 in July and she has small breasts now... she wears a bra everyday and she also carries a little make up bag in her school bag with 2 pads & some underpants as well as some spare change ($3) for just in case she is at a friends after school or somewhere and needs to call me.
I've always been open about things like this so I know she will definitely not hide it from me when she does get her period for the first time. I think when she does, I will take her out somewhere nice for lunch to celebrate her growing up.