My daughter's are older and they use the Sensitive Skin - facial care products by BeautiControl (which I sell) and whatever they see in the Teen magazines that says it is "the" product for pimples. The latter are always passing trends, but they're teens and they have to learn themselves.
You can use a wide variety of products, and whatever she will use daily is the best. However, hormone changes can cause pimples too and that's from the inside, so eating well, sleeping etc will help with that.
On the outside, she needs to keep her face clean with a gentle cleanser (not soap) and exfoliate her face once a week, with a gentle scrub (like St. Ives Apricot Scrub or BeautiControl's scrub). The difference in products is the scent, and quality, and price.
Don't dry her face out, like mine want to do, they see a pimple and want all the oil stopped on their faces, which really makes things worse.
When I was a little older than her, I read all about natural beauty and made my own. My 15 yr old daughter just did this a month or so ago, and it's pretty expensive. And messy. She didn't clean up after she made her papaya, milk, honey facial stuff. But it was a fun way to learn to care for your skin.
Good luck!