In order to treat acne, you have to understand what kind it is. Most people have acne vulgaris, occasional pimples that result from oil/dirt/bacteria getting trapped in the pores and creating a minor infection.
Most of those break-outs are easily treated with good face washings and topical products - benzoil peroxide and salicylic acid are most common in OTC products.
Mine, which I still have as a 30-something adult is cystic. It's deep, painful and unable to be controlled with OTC products. I have to see a dermatologist and be treated with Rx products to keep it under control (antibiotics, topical antibiotics, etc).
If they're willing, I'd have them take her to a dermatologist at least once to see what they recommend. In my experiences, they're quick to recommend over the counter products that most of us are unaware of vs. Rx medications.