I once had (mild) acne. What I did was to completely stay away from many cosmetic products that every tom & dick on the streets was telling me to use. I simply embarked on a thorough home-facial regime. Most likely her/his skin is oily.

Let her wash her face just twice (morn and evening) a day with a "cleansing foam" e.g Simple Nivea products. These are readily available in Supermarkets and they are very mild. Costs around 600-1000 Kshs. Stay away from direct sun.
Let her carry 'wet wipes' during the day, coz thats when dust accumulates on the skin.
She should avoid (at all costs) touching her facial skin with her bare hands unless when washing face.
She should also be very careful if at all she 'exfoliates' coz this worsens acne. If this is done, it should be extra gentle. again I recommend Nivea which has very mild products.(exfoliant is 600/=). Exfoliation to be done not more than 3 times a week.
Let her be patient with this regimen cause the skin takes almost 28 days to respond.

this quite helped me and though i'm a little oily, i'm rarely having break-outs, maybe once in two months, and the 'black-head' spots are slowly fading away.

I hope this helps. Be careful. N/B By the above working for me, doesn't mean it works for everyone.