B.C.
Hello
My son is 11 and a fifth grader. This is the year that they will learn sexual reproduction/education. My son started asking questions a year or two ago, mostly just random things, like "What is a tampon" or "What is gay?" I just answered enough to make him understand. The tampon question came from simply watching commercials!
If she asks questions, I would definately answer them. I wouldn't think she would start her period at 8, unless that is when you or another relative started theirs.
I say just go with her lead!