My dermotologist told me that the worst acne he has ever seen has been on young men taking steriods.  She could have a hormone imbalance.  Genetically, she may have acne-prone skin.  It is expensive to have acne treated, especially for women who usually need hormone therapy in addition to skin therapy and if she doesn't have insurance the treatment may be out of her reach.  It could be a prescription drug.  Maybe she works out and doesn't wash up correctly.  As far as age goes, some people have acne and some don't, age doesn't necessarily matter.  It could be illegal drugs, too, but it's not the number one cause of acne.  A myriad of different things could be causing acne.  Maybe she is having a weird breakout from an allergy from her detergent or soap or perfume or the sun.  I wouldn't jump to conclusions.

Kate

too much laundry detergent
exercising in nylon or wearing nylon underwear or pantyhose

not exfoliating with a bath mitt while showering

I definitely wouldn't jump to illegal drug use as the cause of body acne.
I periodically have acne myself. I take prescription meds and any time any of them is changed (dosage or drug) it shows up on my skin. Sometimes not so bad, other times worse than any outbreak I ever suffered as a teen. Sometimes body and face, sometimes just one or the other, sometimes, strangely, just ONE area of my body (what is up with that?!). It's embarrassing, but it just has to be dealt with. I recently told my doctor "Younger looking skin would be great, but this isn't what I had in mind."