A.P.
Ten year olds in todays world know a lot more (probably misinformed though) about sex and their periods than you might think. It's always good to go the simpliest most direct route. Also, think of things that you thought about before your own period, and address those. With intercourse, that's a little more tricky to give advice on. I don't believe in sex outside of marriage, and was a virgin when I got married at the age of 24. Most parents I would think would want their children to wait until marriage. Present that position first. Also make sure she has all the RIGHT information of STD's. Kids don't think they'll ever get them and more people have an STD than I even want to guess. These are never easy subjects. Good Luck.
P.S. Not trying to judge those who don't wait until marriage.