Oh no! I think I might have been in between 8-10years old when I started getting acne. I had it for like 5-8years after. Its good that you are on top of it, and its sort of better she is getting it younger, because its easier to "train" younger children into a routine.
Anything dove would be the best to use. Since she is so young, her skin is probably sensitive. Witch hazel is a good natural astrigent if you want to do that for astringent instead of dove. If you have a local health food store, they may have natural soap if you are going the natural way.
Please keep us updated. Is her acne bad, or did her first pimple just pop up?
Oh, and to keep her spirits up, you and her should have "facials" once in a while. Just get a gentle mask (or make your own), and do facials with her one night. I remember when I was around 10-12, me and my mom, every once in a while, would do facials together!