One thing most people are unaware of is that the skin is one of the body's biggest detoxification zones. If you put something into your body that your body doesn't like, what it doesn't like will "break" out when it detoxifies through the skin. If she suddenly has started breaking out when she really hasn't before (whether it is around her period time or not), that could indicate that something is off in her body. Could be too much sugar (sweets, pop (high fructose corn syrup), lots of processed foods have added sugar), it could be a food that her body is allergic to or intolerant to--any number of things.
A visit to a Naturopathic doctor and a simple test will let you know if she is allergic or intolerant to any food(s), preservatives, dyes, etc. Many women who have issues around their cycle time (acne or yeast infections) notice a dramatic improvement when they eliminate bread. Why bread? Because either the yeast or the gluten is causing issues/upsetting the delicate gut floral, which the raging hormones at this time are upsetting, causing the flare up in acne as the body works to "get rid" of the offending food.
Drinking lots of water will help cleanse/clean out her system and will help the detox process.
I went to a dermatologist when I was in my teens, twenties, and thirties. When I hit my forties, I started working with alternative healthcare. I discovered I had a lot of food allergies and intolerances--the worst being a casein allergy and severe gluten and soy intolerance--and once I quit eating the foods my body didn't like (or severely cut down on them), I noticed that my Rosacea, eczema on my elbows, and severe acne WENT AWAY! I haven't used anything for acne for the past four years. Not even anything from an alternative healthcare doctor, or over the counter. I mean nothing.
You need to find the ROOT CAUSE for why she is breaking out and attack it from that end. Allopathic doctors will always give you perscriptions and tell you to use over-the-counter meds--it's what they're taught in med school. They aren't taught to get to the root of the problem and cure it. Why? Because they don't make any money that way; you won't be a repeat customer if you take care of the problem, because then the problem goes away! Naturopathic doctors ARE trained to find the root cause of a problem, and then they teach you how to GET RID of the problem by attacking the cause that is manifesting as the problem/issue.
Good luck.