How bad do you think her skin actually is, compared to others of the same age? I speak as another Roaccutane graduate (eventually) but had four or five years before that with lousy skin. Not the worst cystic acne you've ever seen (and thankfully minimal scarring, beyond fairly short lived hyperpigmentation) but significantly different from the kinds of come and go teenage spots my friends have. Tbh, it has dented my confidence for life and you're a lovely mum to be taking this seriously and looking for advice.
Did you have teenage acne? Or any history of PCOS? In my case I think this is what caused it. My PCOS is otherwise mild, visible only on an ultrasound of the ovaries and not (in 30s anyway) detectable from blood tests. But it can really fuck with your skin. For me, I think the pill might have been a better treatment than the multi-year courses of antibiotics I was prescribed (wrecked my digestion) or Roaccutane which made me depressed and (I still worry) might have done damage to my liver, especially when unwisely combined with first year of university drinking! Of course, the pill is not a small step and probably not to be recommend for mild/ moderate teenage acne of under a year's duration. But could you ask your doctor (esp if she also has very irregular periods, though maybe she's too young to be sure of that) to run a basic test for androgen/ estrogen levels?
The best thing for now would probably be a tretinoin gel. Benzoyl peroxide is harsh stuff. It bleached all of our pillow cases and made my skin super inflamed and red, probably worse than it was to begin with. Of course, skin type varies. Mine is naturally prone to over-reaction (hives, super-swollen bites etc). You can order some of these things on the internet with a prescription provided by the internet pharmacy. I might try this, if I didn't have a sympathetic GP: https://e-surgery.com/product/treclin-gel/?gclid=EAIaIQobChMI1KSu48XL9QIV9RSLCh2GFwHOEAQYASABEgLEoDD_BwE
Also, if your GP isn't sympathetic, change GPs. Mine was totally hopeless, 'you'll grow out of it etc' and in the end my parents paid privately, years on, to see a dermatologist. In fact the spots themselves weren't the end of the world. The worst thing for me (naturally introverted) was that embarrassment about the spots prevented me from taking part in a lot of normal teenage social life and some sports activities (swimming!), and this has (for me, perhaps unusually bashful) had lifelong consequences.