This never really worked for me as a teenager either. I've suffered with my skin for years and have tried so many things prescribed and drug store so I can help with what helped me.
Please please tell her that even if she has the urge - don't touch her face, don't pick the spots! It's such a minor thing but makes such a difference. Once you start picking, it only really gets worse.
If she is up for trying to the contraceptive pill, this may help but a reminder that whenever she would eventually come off of the pill that the skin may flare up again.
If she has oily skin - Cetaphil face wash - Oily Skin Cleanser, morning and night. If she has drier skin, Cetaphil face wash - gentle skin cleanser.
If her skin is sore at the moment, a light rose water will do her the world of good. I used to find the Garnier Rose Water really helped with calming any angry spots down and it doesn't dry out your skin.
A Tea Tree Moisturiser - Superdrug do a good value one about £3.99. They do a day one and a night one, apply this after face wash > toner > then moisturiser.
If she has any spots that she has already picked then Sudocrem genuinely does work with the picked spots that may be scabby (heals them slightly quicker)
Any big boil spots - the zit stickers can help at night and it deters you from picking at your face also!
Niacinamide is a massive game changer. A Niacinamide serum would be helpful to apply possibly every other night, this would fit in after the toner stage. You can find drug store Niacinamide serums that have helped me, the one I found helped me the most is the revolution super strong one but obviously as a beginner, get the one that's not quite as strong. Again very affordable (bottle less than £10) and lasts forever. Or you can wash your face, apply serum and then moisturise. I would say in the mornings just do a face wash and a moisturise.
If she can continually do some of these stages at least, I'm almost sure she will see a massive improvement. She may have a flare up because she's just started her period but her skin will calm down in a few months!
I definitely would NOT recommend roaccutane- this is a LAST option after years of terrible terrible acne.
As much as people aren't ever sure it's true, how much sugar you eat really make a difference - less sweet food does help (I found with me anyway) and drinking water will keep your skin hydrated.
This is coming from me (I'm not a professional) but I'm 28 and my skin is pretty clear now, I've tried almost everything and I suffered with acne from that age of 14 so know exactly how she feels and how insecure it can make you feel. Please don't feel like you have to spend 100s on the best skin care. If I could go back the one thing I would tell myself is don't pick the spots. I found later In life that the simple things genuinely did work in the end, and keeping up with the right skincare routine.
Keep your skin moisturised and don't overwash. I hope this helps!